Class 7 Physics - Light

What is reflection of light?

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Name two types of spherical mirrors.

A spherical mirror is a mirror which has the shape of a piece cut out from a huge sphere.

There are two types of spherical mirrors: Concave and Convex

Define Lateral inversion.

Lateral inversion - The phenomenon of left side appearing right side and
right side appearing left side on reflection in a plane mirror is called
lateral inversion

State two uses each of : plane mirror

Uses of Plane mirror -
(a) They are used as looking glass
(b) They are used by opticians to increase the effective length of the
room by keeping two mirrors on the opposite walls of the room

Reflection is the __________ of light off a surface.

Reflection is the bouncing of the light off a surface which helps in forming an image of an object.

Fill in the blanks :
A plane mirror forms a ................... and ................... image.

Virtual and erect.

Plane mirrors are the only type of mirror for which a real object always produces an image that is virtual, erect and of the same size as the object.

List some characteristics of plane mirror.

When a ray of light falls on a surface, then it can undergo one of the following three phenomenon reflection, refraction or absorption. When it falls on a normal surface then most of the light gets absorbed. So mirrors are polished surfaces coated with mercury such that they reflect most of the light falling on them. Now based on the type of reflecting surface we can classify mirrors as concave, convex or plane mirror. Here we will be talking about plane mirror only. So two form an image we require at least two rays from the object which meet or appear to meet at a point. In case of the plane mirror, here we have used three images for better clarity in the ray diagram shown below

For the ray starting from point A and traveling in horizontal direction towards point E, the angle of incidence is 0 and hence it retraces its path. Similarly the ray starting from A and travelling towards point C, follows law of reflection. When these rays are produced backward they appear to meet at a point E and D. Now this image is known as virtual image. What is the difference between real and virtual image? In real image the rays of light actually meet after reflection while in virtual image it appears to meet but not actually meet. Real image can be obtained on screen but not virtual image.

Characteristics of the image formed by a plane mirror :

It is virtual
It is erect and of same size as the object
The distance of object from the plane mirror is same as the distance of image from the plane mirror.

One of the important characteristic of the image is that it is laterally inverted. It means if you raise your left hand it would appear in the plane mirror that you have raised your right hand.

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An image that cannot be obtained on a screen is called a________ (real, virtual) image.

An image that cannot be obtained on a screen is called a virtual image

We know that for an image to be obtained on a screen , rays should intersect on the screen, but a virtual image is formed by rays that do not meet. Hence, it is not possible to obtain a virtual image on the screen.
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Is the image formed by the plane mirror exactly of the same size as the object?

Yes.

Followings are the characteristics of image formed by plane mirror:

It is virtual and erect and laterally inverted.
Magnification is unity i.e. size of image is equal to size of object.
Image can't be obtained on screen.
Distance of image from mirror is equal to distance of object from mirror.

What is a virtual image? Give one situation where a virtual image is formed.

The image which cannot be taken on a screen is called virtual image. When some object is placed very close to the concave mirror we don't get any image on the white screen placed behind the mirror. Such image is called virtual image.

Image obtained on a screen is called _______ image.

The image obtained on a screen is called a real image.

An image is defined as the collection of focus points of light rays coming from an object. A real image is the collection of focus points actually made by converging rays, while a virtual image is the collection of focus points made by extensions of diverging rays.

What is a mirror ?

Mirror is a polished or smooth surface (as of glass) that forms images by reflection. It reflects light in such a way that, for incident light in some range of wavelengths, the reflected light preserves many or most of the detailed physical characteristics of the original light.

What is the difference between virtual images produced by concave, plane and convex mirrors ?

The virtual image formed by concave mirror is magnified, that produced by plane mirror is of the same size and that by a convex mirror is diminished.

Hence, this is the difference between virtual images produced by concave, plane and convex mirrors.

Look at figure. Can the image of the child in it be obtained on a screen? (Yes/No)

No, the image of the boy formed cannot be obtained on a screen because the image formed by a plane mirror is always a virtual image.

For driving a car what type of mirror would you prefer to see traffic at your back and
why ? (Convex/Concave)

We prefer convex mirror because it provides wide range of view and erect image.

A real image is always .......(inverted/ magnified).

A real image is always inverted. It may or may not be magnified depending on the position of the object.

Can a real image be formed with the help of a plane mirror?

Yes, a plane mirror can form a real image. A plane mirror can form a real image only for a virtual object. Let us understand what is a virtual object. Object is nothing but the point of intersection of incident rays. The object is real if the incident rays actually meet. The object is virtual if the incident rays appear to meet (but not actually meet).

So in this case, these converging rays of incident light intersect at a point after reflection to give a real image.

Give reasons:
Concave mirrors are used in solar devices.

Concave mirrors are used in solar devices to collect heat and radiations.Heat radiations from the sun coming from infinity are brought to focus by concave mirror in its focal plane.

If you stand in front of a big mirror and lift your left hand, which hand will your image in the mirror appear to lift ?

In an image formed by a mirror, the left of the object appears on the right and the right appears on the left. This is known as lateral inversion. So, if you stand in front of a big mirror and lift your left hand, the right hand will appear to be raised in the mirror.

What is the angle, in degrees, between a plane mirror and the straight line joining the object and its image?

The image formed by the plane mirror is always perpendicular to the plane mirror. So, the line joining by object and image is perpendicular to the plane mirror.

Hence, the angle between a plane mirror and the straight line joining the object and its image is $$90 ^{\circ}$$.

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State three differences between a real image and virtual image.

Real Image Virtual Image

1. Real image can be obtained on screen 1. virtual image cannot be obtained on screen

2. real image is formed by actual 2. virtual image is formed by just extending the refracted rays backward.

meeting of rays after refraction

3. real image is always inverted 3. virtual image is always erect.

Explain why a real image can be projected on a screen but a virtual image cannot.

As we know real image is formed by real intersection of rays hence it is possible to project it on screen whereas virtual image is drawn via back tracing the path of reflected rays hence they dosen't meet in reality so they can"t be projected on a screen.

Show an experiment which proves light always travels in a straight line.

Showing an experimental view that proves light always travels in a straight line.

The demonstration of the pin-hole camera. See image.

A pinhole camera is a simple camera without a lens but with a tiny aperture, a pinhole-effectively a tight proof box with a small hole in one side light from a scene passes through the aperture and projects an inverted image on the opposite side of the box, which is known as the camera obscure effect.

Perform an experiment taking tree wooden planks(small-sized) made a small ole in all the three planks in the center. I arranged all the three one after the other in straight, having a space of some distance between each plank, then I lit a candle and placed it before the first plank and asked one of my friends to see through the hole from the third plank. He can clearly see the candle flame, then what I did is move one of the planks (second) and he could not see the flame. It proves that the light travels in a straight line, the same phenomena take place in the Pinhole camera.

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Give the reason for the following: Concave mirrors are used as shaving mirrors.

When an object is placed in between the pole and the focus of a concave mirror, a virtual, enlarged, and erect image is formed. A person sits close to the shaving mirror. Therefore, he sees a magnified and erect image of himself behind the mirror which helps him in shaving.
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Write down the letters of the word 'PHYSICS' as seen in a plane mirror held perpendicular to the plane of the paper.

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Write three differences between a real image and a virtual image.

$$\underline{\text{Real Image}}$$	$$\underline{\text{Virtual Image}}$$
(i) Real image can be taken on a screen	(i) Virtual image cannot be taken on a screen
(ii) The rays of light physically intersect to form a real image	(ii) The rays of light do not physically meet to form a virtual image
(iii) It is always inverted	(iii) It is always erect

State two uses of a convex mirror.

Uses of Convex mirror -

(a) It is used as a reflector in street lamps as it diverges the light rays
over a wide area.

(b) It is used as a rear view mirror in vehicles because it forms an erect
and highly diminished image irrespective of the position of the
traffic behind.

State two uses of a concave mirror.

Uses of Concave mirror -
(a) Concave mirror is used to collect heat radiations in solar cooker
(b) It is used as a shaving mirror as it produces highly magnified
image when the face of a person is placed between pole and focus

Boojho stands at A just on the side of a plane mirror as shown in Fig.. Can he see himself in the mirror? Also can he see the image of objects situated at P, Q and R?

Boojho can see image of an object if the reflected ray can reach his eyes. Reflected rays from P and Q can reach the eyes of Boojho, hence he can see P and Q. Reflected rays from A move away from him and never reach his eyes. Hence, he cannot see his own image. Reflected rays from R pass from under his eyes and hence he is unable to see R too.

Name the type of mirror used in the following situations:
a) Headlights of car
b) Solar furnaces

a) Headlights of car: Type of mirror used is concave as the light of lamp undergoes divergence from reflector surface and cover large area in the front.

b) Solar/rear view of vehicle: It is a convex mirror as it gives diminished, virtual and an erect image of the side or rear with wider field of view. A convex mirror enables driver to view much larger area than would be possible with a plane mirror.

c) Solar Furnace: It is a concave mirror. As sun rays after reflection from its surface, get converged at focus with much intense heat.

State the types of mirrors used for (i) headlights and (ii) rear view mirrors, in cars and motorcycles. Give reason to justify your answer in each case :

(i) Concave mirror is used in the headlights of vehicles as a reflector. Bulb is placed at the focus of concave mirror so the light rays coming from bulb are collected and after reflection we get a strong beam of light .

(ii) Convex mirror is used as rear view mirrors in vehicles , the other vehicles are always beyond the $$2F$$ of convex lens so we get a diminished and erect image of other vehicle on lens hence lens gives a larger field of view to us , and we can see more vehicles in lens .

When used for its intended purpose, a make-up mirror causes a person's face to look larger and right-side-up. What kind of mirror is a make-up mirror and where should the person be located relative to the focal point (f) to get the desired image?

Makeup mirrors are concave mirrors in which the face should be in between mirror and its focal length to form virtual,erect and magnified image.

At an instant, a watch shows time $$2: 35$$ when seen through the mirror, what time will be appeared?

Current time given $$2:35$$.

Due to reflection by a plane mirror, the clockwise watch is converted into an anticlockwise watch which is shown in the figure.
So, time will appear to be $$10:25$$ in the plane mirror.

How do you appreaciate the role of spherical mirrors in daily life?

There are many applications of spherical mirrors in our day-to-day life.

1.Shaving mirror

2.Rearview mirror in vehicles

3.In flashlights

4.In headlights

And there are so many more

Name equipment where the following are used :
a. A concave mirror
b. A convex mirror

a) Satellite dishes use concave mirrored surfaces to receive and redirect signals. Headlights, flashlights, and camera flashes use concave mirrors to focus beams of light.

b) Convex mirrors are used in automobile side and rearview mirrors. Some cell phones are also equipped with these mirrors to aid users when performing a self-portrait shot.

Which type of mirror is used in head lights of vehicles?

Concave mirrors are used in head lights of vehicles because when the bulb of headlight is placed at focus of concave mirror it will allow the light to spread out to infinity after the reflection on the mirror.

A plane mirror lying on the ground is not visible from all directions. But a piece of paper can be seen from any direction. Explain.

Paper can be seen from any direction because the light that hits the page reflects in all directions.(Paper being rough surface shows diffused reflection) But for mirror, parallel rays will not be reflected in all directions (mirror being a smooth surface it shows regular reflection )hence it won't be visible from all directions.

If a mirror reverses right and left, why does not it reverse up and down?

The mirror does not reverse images from left to right, it reverses them from front to back relative to the front of the mirror. Stand facing a mirror. Point to one side. You and your mirror image are pointing in the same direction. Point to the front. Your mirror image is pointing in the opposite direction to you. Point upwards. You both point in the same direction. Now stand sideways on to the mirror and repeat. You are now pointing in opposite directions when you point sideways. Place the mirror on the floor and stand on it. This time you point in opposite directions when you point upwards and your upside down image points downwards. In all cases the direction reverses only when you point towards or away from the mirror.

Why driver prefers to use a convex mirror as rear-view mirror?

We use convex mirror as a rear view mirror in the vehicles because convex mirror always forms virtual, erect and diminished images irrespective of distance of the object. A convex mirror enables a driver to view large area of the traffic behind him. Convex mirror forms very small image than the object. Due to this reason convex mirrors are used as rear view mirrors in vehicles.

Write the differences between convex and concave lens.

Convex lens: Concave lens:

(1)The converging lens in air. (1)The diverging lens in air.

(2)The principal focus behind the lens. (2)Principal focus is infront of lens.

(3)Used as magnifying lens. (3)Used as rear view mirror.

(4)Forms both real and virtual images. (4)Only form virtual image.

Give the uses of a concave mirror.

Concave mirror is used in flashlights,torch etc as it has the diverging property, it is also used by the dentist for clear view of tooth and cavities inside the mouth by giving magnified view.

What is reflection of light? Explain reflection of light with the help of an activity?

When light rays fall on a highly polished (e.g. mirror) smooth surface and return to the same medium, it is called reflection of light.
Activity to show reflection of light: This activity should be done at night or in a dark room. Ask your friend to hold a mirror in his hand at one corner of the room. Stand at another comer with a torch in your hand. Cover the glass of torch with your fingers and switch it on. There should be small gap between your fingers. Direct the beam of torch-light on to the mirror that your friend is holding. Adjust the direction of torch so that patch of light falls on your friend standing in another corner of the room. This activity shows the reflection of light also that light travels in straight line.

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How would you define reflection of light?

When light rays after striking a smooth and shiny surface return to the same medium, this phenomenon is called the reflection of light.

Draw ray diagrams to show the formation of three times magnified (a) real, and (b) virtual image of an object by a converging lens. Mark the positions of O, F and 2F in each diagram.

$$\text(A)\ $$ When the object is placed between $$2F$$ and $$F$$ then the image is real, inverted and enlarged.

$$\text(B)\ $$When the object is placed between $$F$$ and the optical centre, the image is virtual, erect and enlarged.

Have you ever seen an ambulance? It is written in the form of mirror image on vehicles. Explain why it is done so and give the mirror image of AMBULANCE.

The mirror image of AMBULANCE is written so on the vehicles for the people to see in their rear view mirrors, read it correctly and immediately give way to the vehicles as it carries patients who need urgent medication.

What do we need in order to see a shadow?

We need:

(i) A source of light,

(ii) A screen

(iii) An opaque object.

State any two differences between Convex and Concave mirrors.

Convex mirror always forms virtual, upright and diminished image.

Concave mirrors forms real and inverted image for object distance greater than its focal length and forms virtual and upright image for object distance less than focal length.

Find out the letters of English alphabet or any other language known to you in which the image formed in a plane mirror appears exactly like the letter itself. Discuss your findings.

Letter like A, H, I, M, O, T, U, V, W etc. appear same when through a plane mirror.

If an object is placed at a distance of $$10\ cm$$ in front of a plane mirror, how far would it form its image?

The plane mirror forms a virtual, erect image behind the mirror at the same distance as the object's distance in front of the mirror.

So, the plane mirror forms an image at a distance of $$10 \ cm$$ behind the mirror.

Light travels in .............................. (curved/straight) lines.

Light travels in straight lines. Shadows are evidence of light travelling in straight lines.
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What kind of mirror is used in big shopping stores to watch the activities of customers ?

'Convex Mirror' is used in shopping stores to watch the activities of customers. This is because the convex mirror has large field of view.

Write down the letters of the word CAPITAL as they appear in a plane mirror held perpendicular to the plane of paper.

The image of the alphabets will be laterally inverted. At the same time, the image distance of an alphabet must be the same as the distance of the alphabet from the mirror.
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A man stands in front of a mirror of a special type.He finds that his image has a very small head,a fat body and legs of normal size.What can be the shapes of the three parts of the mirror?

The shapes of the three parts of the special mirror are:

Convex mirror at the top as head size is diminished.
Concave mirror in the middle as the body size is enlarged.

Plane mirror at the bottom as the size of legs are same.

Define Reflection.

The bouncing back of light from any shiny surface is known as reflection.

For example, the image that we see in a mirror, water or any shiny surface.

Name the type of mirror used in the following situations.
Headlights of a car
Side/rear - mirror of a vehicle
Solar furnace
Support your answer with reason

Headlights of a car - concave mirror - Because bulb lies in the focal point of the mirror by using concave mirror light rays travel parallel and reach maximum distance

Rear - mirror of a vehicle- convex mirror - Because convex mirror diminishes the image and can cover much more area than any other mirror

Solar furnace - concave mirror - Concave mirror concentrates sun rays to a point that increases energy at the focal point.

What do you mean by reflection of light?

Reflection:- Reflection is the bouncing of light when it strikes a surface.

When light strikes a surface, some part of the light will come back to the same medium as the incident one. This phenomenon is called reflection.

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Write two uses of spherical mirrors.

Following are the important uses of spherical mirrors:

The concave mirrors are commonly used as shaving mirrors because when we see our face in the concave mirror then an enlarged and erect image is formed which helps in smooth shaving.
A concave mirror is used as the reflector in search lights, head lights of motor vehicles, solar cookers, torches and in table lamps.
A convex mirror is used in automobiles such as scooters, trucks and buses as rear view mirror to see the traffic behind the vehicle. The reason for it is that a convex mirror has a much wider field of view and the images formed are smaller and erect.

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A point '$$O$$' marked on the surface of a glass sphere of diameter $$20cm$$ is viewed through glass from the position directly opposite to the point '$$O$$'. If the refractive index of the glass is $$1.5$$, find the position of the image formed. Also, draw the ray diagram for the formation of the image.

for $$S_2$$

$$u=-20cm$$

$$R=-10cm$$

$$\displaystyle\frac { u_{ 2 } }{ V } -\frac { u_{ 1 } }{ u } =\frac { u_{ 2 }-u_{ 1 } }{ R } $$

$$\displaystyle \frac { 1 }{ V } -\frac { 3 }{ 2(-20) } =\frac { (1-3/2) }{ -10 } $$

$$\displaystyle\frac { 1 }{ V } =\frac { 1 }{ 20 } -\frac { 3 }{ 40 } =\frac { -1 }{ 40 } $$

$$\boxed { V=-40cm } $$

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Draw a ray diagram to show the formation of image of an object placed between the pole and focus of a concave mirror . State the position, size and nature of the image

OBJECT LIES BETWEEN FOCUS AND POLE :
A virtual erect and bigger image is formed behind the mirror
Image formed A'B' is on the other side of mirror $$ \leftarrow $$ position
Enlarged (magnified) $$ \leftarrow $$ size
Virtual and erect $$ \leftarrow $$ nature
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An object is placed at a distance of $$30$$ cm from a concave lens of focal length $$30$$ cm.
(i) Use lens formula to determine the distance of the image from the lens.
(ii) List four characteristics of the image (nature position, size, erect/inverted) in this case.
(iii) Draw a labelled diagram to justify your answer apart (ii)

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Write various uses of concave mirror in everyday life

various uses of the concave mirror in everyday life are :

• Used as a shaving mirror.
• Used as a makeup mirror.
• Doctors used as head mirrors.
• On film projectors.

Distinguish between a real and a virtual image of an object. What type of image is formed
(i) by a plane mirror, (ii) on a cinema screen ?

A real image is formed by the actual intersection of light rays whereas a virtual image is formed by the imaginary intersection of light rays.

(i) In plane mirror the image is formed due to virtual intersection of the light rays behind the mirror.

(ii) On a cinema screen, real image is formed due to actual intersection on the cinema screen.

What is the important difference between looking at a photograph of your face and looking at yourself in a plane mirror?

Image of our face in a plane mirror is laterally inverted, so left is right and right is left. However, in a photograph of our face this is not the case.

What is the difference between a real image and a virtual image? Give one example of each type of image.

Real image can be obtained on a screen because light rays actually pass through a real image but virtual image cannot be formed on screen because light rays do not actually pass through a virtual image.
Example:
The Image formed on a cinema screen is an example of a real image.
The image formed on a plane mirror is a virtual image.

A man stands 10 m in front of a large plane mirror. How far must he walk before he is 5 m away from his image?

Initially, the distance between the man and the mirror is 10m. So, the distance between man and image is 10+10=20m.
Distance between the man and his image is 5m when the man is 2.5m away from the mirror.
Therefore, he has to walk 10m -2.5m=7.5m towards the mirror.

(a) A boy with a mouth 5 cm wide stand 2 m away from a plane mirror. Where is his image and how wide is the image of his mouth ?
(b) The boy walks towards the mirror at a speed of 1 m/s. At what speed does his image approach him?

(a) The image will form 2 m/s behind the mirror and the width of the image of the boy's mouth will be 5 cm.
(b) When the boy walks towards the mirror at a speed of 1 m/s, his image will also appear to move towards the mirror at the same speed of 1 m/s. So, the speed at which his image approach him will be 2 m/s + 2 m/s =4 m/s.

Name the two types of spherical mirror. What type of mirror is represented by the:
(a) back side of a shinning steel spoon?
(b) front side of a shinning steel spoon?

Two types of spherical mirrors are:
(i) concave mirror
(ii) convex mirror
Type of mirror represented by the
(a) back side of a shinning steel spoon - convex mirror
(b) front side of a shinning steel spoon- concave mirror.

What information do we get about sunlight from the formation of a rainbow?

Rainbow is also known as the spectrum of light which is formed when white light splits into its constituent seven colours. So, From a rainbow, we can say that sunlight consists of seven colours.

The diagrams show the appearance of a fork when placed in front of and close to two mirrors A and B, turn by turn.
(a) Which mirror is convex ?
(b) Which mirror is concave ?
Give reasons for your choice.

(a) Mirror B is convex since it forms a smaller mage of fork.
(b) Mirror A is concave since it forms a larger image of fork.

Give two uses of a convex mirror. Explain why you would choose convex mirror for these uses.

Two uses of convex mirror.

(i) A convex mirror is used as a rear view mirror in vehicles because it forms erect and diminished images of the objects and has a wider field of view.

(ii) Big convex mirror are used as security mirror in shops so that a large number of goods displayed in the shop can be seen in the convex mirror.

What type of mirror could be used as a dentist's mirror ?

The dentists use concave mirrors to see large images of the teeth of patients.

When an object is placed between the pole and focus of a concave mirror, the image formed will be virtual, erect and magnified,

(a) Explain why, through both a plane mirror and a sheet of paper reflect light, but we can see the image of ur face in a plane mirror but not in a sheet of paper.
(b) The image in a plane mirror is virtual and laterally inverted. What does this statement mean ?
(c) Write all the capital letter of the alphabet which look the same in a plane mirror.

(a) We see the image
of our face in a plane mirror but not in asheet of paper because images are
formed by regular reflection of light and in the case of a plane mirror,
regular reflection takes place, while in the case of a sheet of paper, diffuse
reflection takes place

(b) The image is virtual and laterally inverted means it cannot be obtained on a screen and is reversed sideways.

Where in nature can you find evidence that white sunlight may be made of different colours?

We know that sunlight is white. And during rainy days we see formation of rainbow (a band of seven colors) from this white sunlight after passing through water droplets in air. hence the formation of rainbow suggests that White Sunlight is made of different colours.

Name the scientist who discovered that sunlight consists of seven colours.

Isaac Newton

What type of mirror could be used :
(a) as a shaving mirror ?
(b) as a shop security mirror ?

(a) Concave mirror: The shaving mirrors are used to view the enlarged image of the face.
(b) Convex mirror: The reflective surface bulges outwards toward the light source which results in a distorted image but an expanded field of view.

A man sits in an optician's chair, looking into a plane mirror which is 2m away from him and views the image of a chart which faces the mirror and is 50cm behind his head. How far away from his eyes does the chart appear to be?

Distances between the man and the mirror= 2cm
Distances between the man and chart = 50cm=0,5m
Distance between the chart and mirror = 0.5m+2m= 2.5m
Distance between mirror and the image of the chart=2.5m
Distance between man and the image of chart= distance between man and the mirror +Distances between mirror and the image of the chart=2m+2.5m=4.5m

A person wants to see the full-length image of a tall building in a small mirror. Which type of mirror should be used by him?

The person will use a convex mirror because it always forms a virtual, erect and diminished (small-sized) image, and has a wider field of view which will help in capturing the whole building.

The figure shows the image of a tall building in a convex mirror.

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What is the distance between the image and the plane mirror, if the object is at $$15\ m$$?

In plane mirror, the distance between object and mirror is same as the distance between the image and mirror.

$$\Rightarrow$$ Image Distance $$=$$ Object Distance

$$ \therefore $$ Distance between image and plane mirror is $$15\ m$$.

Write one use of such mirror images on a daily basis. Write STOP as it should written on the front of a police car.

This is due to the phenomenon of refraction. Light reflected from the fish travels through the water towards the eye. As it passes from the water into the air, it refracts away from the normal because water is denser than air and thus, the fish appears closer.

List two characteristics of the images formed by plane mirrors?

(i) Image formed by a plane mirror is always virtual and erect.

(ii) The size of the image is equal to that of the object.

(iii) The image formed is as far behind the mirror as the object is front of it.

(iv) The image is laterally inverted.

What type of image is formed on a cinema screen?

As we have seen that, In the theater, light beams are projected on the screen with the help of projector. As we know that real images can only be collected on the screen. So we can say that 'image formed on a cinema screen is always real.

What type of mirror is used as a side mirror in scooter? Why is this type of mirror chosen?

Mirror used as a side mirror in a scooter is 'convex mirror'. The convex mirror forms as a diminished image of an object which is helpful for the driver to cover a wide area of view.

What type of image is formed in a plane mirror?

Images formed by plane mirrors are virtual, upright, left-right reversed, the same distance from the mirror as the object's distance, and the same size as the object.
1698325_1786204_ans_69f51678ffb2423394fcf5e0efcb1373.jpg

1698325_1786204_ans_69f51678ffb2423394fcf5e0efcb1373.jpg

The side mirror of a scooter got broken. The mechanic replaced it with a plane mirror. Mention any inconvenience that the driver of the scooter will face while using it?

Mirror used as a side mirror in a scooter is convex mirror. Inconveniences are
i) Less area visible on plane mirror as compared to convex mirror.
ii) Unable to see traffic behind the vehicle.

Differentiate between virtual image formed by a concave mirror and of a convex mirror.

The virtual image formed by a concave mirror is always magnified whereas the virtual image formed by a convex mirror is diminished.

Boojho planned a activity to observe an object A through pipes as shown in Fig. 16.8, so that he could see objects which he could not directly see.
(a) How many mirrors should he use to see the objects?
(b) Indicate the positions of the mirrors in the figure.
(c) What must be the angle with respect to the incident light at which he should place the mirrors?
(d) Indicate the direction of rays in the figure.
(e) If any of the mirrors is removed, will he be able to
see the objects?

(a) Three Plane mirrors

(b) As shown in fig-

(d) As shown in figure-

(e) No, he will not be able to see the objects.

1647207_1790789_ans_0a8339f896234972b8385610b4007832.png

Fill in the blanks:
A plane mirror _______ reflect 100 percent light falling on it.

A plane mirror does not reflect 100 percent light falling on it.

Domestic mirrors are not perfect mirrors as they absorb a significant portion of the light which falls on them, A simpler mirror may reflect 99.9% of the light

Fill in the blanks:
The image formed by a plane mirror is erect and ______.

The image formed by a plane mirror is erect and virtual.

The concave reflecting surface of a torch got rusted. What effect would this have on the beam of light from the torch?

if the concave reflecting surface of a torch gets rusted ,it will not produce clear beam of light and it will produce light with lower brightness, so the object will also be not clearly visible in lower brightness or light.

A short object of length $$L$$ is placed along the principal axis of a concave mirror away from focus. the object distance is $$u$$. If the mirror has a focal length $$f$$, what will be the length of the image? You may take $$L<< \left| v-f \right| $$

As the mean distance of object from mirror is $$u$$
$$\therefore$$ $${u}_{1}=u-\cfrac{L}{2}$$ and $${u}_{2}=(u+\cfrac{L}{2})$$
Let the image of the two ends of object form at distance $${v}_{1}$$ and $${v}_{2}({v}_{1}> {v}_{2})$$. So lenght of image on principle axis is $$L'({v}_{1}-{v}_{2}$$)
$$\cfrac { 1 }{ v } +\cfrac { 1 }{ u } =\cfrac { 1 }{ f } $$ or $$\cfrac { 1 }{ v } +\cfrac { 1 }{ f } =\cfrac { 1 }{ u } $$
$$\Rightarrow$$ $$\cfrac { 1 }{ v } =\cfrac{u-f}{uf}\Rightarrow v=\cfrac{uf}{u-f}$$

So $$L'={v}_{1}-{v}_{2}==\cfrac { \left( u-\cfrac { L }{ 2 } \right) f }{ \left( u-\cfrac { L }{ 2 } \right) -f } -\cfrac { \left( u+\cfrac { L }{ 2 } \right) f }{ \left( u+\cfrac { L }{ 2 } \right) -f } \Rightarrow L'=f\cfrac { u-\cfrac { L }{ 2 } }{ \left( u-f-\cfrac { L }{ 2 } \right) } -\cfrac { u+\cfrac { 1 }{ 2 } }{ \left( u-f+\cfrac { L }{ 2 } \right) } $$

$$=f\left[ \cfrac { \left( u-\cfrac { L }{ 2 } \right) \left( u-f+\cfrac { L }{ 2 } \right) -\left( u+\cfrac { L }{ 2 } \right) \left( u-f-\cfrac { L }{ 2 } \right) }{ \left( u-f-\cfrac { L }{ 2 } \right) \left( u-f+\cfrac { L }{ 2 } \right) } \right]$$

$$ =\cfrac { f\left[ { u }^{ 2 }-uf+\cfrac { uL }{ 2 } -\cfrac { uL }{ 2 } +\cfrac { fL }{ 2 } -\cfrac { { L }^{ 2 } }{ 4 } -\left( { u }^{ 2 }-uf+\cfrac { uL }{ 2 } -\cfrac { uL }{ 2 } +\cfrac { fL }{ 2 } -\cfrac { { L }^{ 2 } }{ 4 } \right) \right] }{ { \left( u-f \right) }^{ 2 }-\cfrac { { L }^{ 2 } }{ 4 } } $$

$$\therefore L<<(u-f)$$
So neglecting the terms $$\cfrac { { L }^{ 2 } }{ 4 } $$
$${ L }^{ 2 }=f\left[ \cfrac { \cfrac { fL }{ 2 } +\cfrac { fL }{ 2 } }{ { (u-f) }^{ 2 } } \right] \quad \quad $$
$$L'=\cfrac { ffL }{ { (u-f) }^{ 2 } } \Rightarrow L'=\cfrac { L{ f }^{ 2 } }{ { (u-f) }^{ 2 } } $$
it is the length of image $$f$$

The image formed by a plane mirror is at a distance behind the mirror as _____________.

For plane mirrors, the object distance (often represented by the symbol $$d_o$$) is equal to the image distance (often represented by the symbol $$d_i$$). That is, the image is the same distance behind the mirror as the object is in front of the mirror.

What do you mean by the term reflection of light?

Reflection of light - When light strikes a polished surface It comes back in the same medium, which is called reflection of light.

Name the mirror which always forms an erect and virtual image. What is the size of the image as compared to that of the object ?

Convex mirror always produces erect and virtual images of an object kept at any position in front of it. The images formed are diminished, i.e. the size of the image is shorter than the size of the object.

How do we see objects around us?

The light rays propagate in a straight line. When any object comes in its path of propagation, it bends back or reflects back alter striking the object. The reflected rays come to our eyes and we see the objects around us.

What is meant by lateral inversion of an image in a plane mirror ? Explain it with the help of a diagram.

Lateral inversion is the interchange of the left and right sides in the image of an object in a plane mirror.
The diagram shown indicates the image formation of a letter P in a plane mirror, where the letter appears laterally inversed.
1699452_1800081_ans_424f941b544142d79e673137e11b95bd.png

1699452_1800081_ans_424f941b544142d79e673137e11b95bd.png

Write three characteristics of image formed by a plane mirror ?

The three characteristics of image formed by a plane mirror :

Image formed are upright or erect
Images formed are virtual
Images formed are of the same size as the object

Distinguish between a real and a virtual image.

Real image	Virtual image
1. A real image is formed due to actual intersection of refracted (or reflected) rays.	1. A virtual image is formed when the refracted (or reflected) rays meet if they are produced backwards.
2. A real image can be obtained on a screen.	A virtual image cannot be obtained on a screen.
3. A real image is inverted with respect to the object.	A virtual image is erect with respect to the object.

1706699_1806586_ans_800cbe559f8c4a2ebe2add298e37522d.png

State four characteristics of the image formed by a plane mirror.

(i) The Image is erect.
(ii) The Image is of the same size as that of the object.
(iii) The image is laterally inverted. Right side appears to be left and left side appeared to be right.

(iv) The image is virtual.

Name the two kinds of spherical mirrors and distinguish between them.

The two kinds of spherical mirrors depending upon whether the inner or outer surface of the sphere is silvered are :

Concave mirror
Convex mirror
Concave mirror Convex mirror
Outer surface is silvered Inner surface is silvered
Reflection takes place from hollow surface . Reflection takes place from bulging surface

Name the spherical mirror which converges the beam of light incident on it. Justify your answer by drawing a ray diagram.

$$\large \textbf{Concept used:}$$

Converging nature of concave mirror

$$\large \textbf{Correct answer: Concave mirror}$$

$$\large \textbf{Explanation:}$$

$$\bullet$$ Since the $$concave$$ mirror is curved inwards, so it converges the light incident on it.

$$\bullet$$ The reflected rays follow the $$laws \ of \ reflection$$.

$$\bullet$$ The converging nature of the concave mirror can be seen when we try to focus the rays from the sun at a spot. This spot of light is the image of the Sun on the sheet of paper. This point is the $$focus$$ of the concave mirror. The heat produced due to the concentration of sunlight ignites the paper.

2128631_1807966_ans_962ce60828f447bcb8e5e341b0816edb.png

What are the properties of image formed by a plane mirror?

- Image is virtual and erect
.- Size of the image is equal to that of object
- Image is laterally inverted.
- The image formed by a plane mirror is always at the same distance as the object is in front of it.

Two plane mirrors are placed making an angle $$ \theta $$ in between them. For an object placed in between the mirrors , if angle is gradually increased from $$ 0^{\circ} $$ to $$ 180^{\circ} $$, how will the number of image ; increase , decrease or remains unchanged ?

The number of image decreases as the angle between the two mirror increases from 0 to 180 this is due to decrease in number of reflection.

Answer the following question.
Why are the mirrors fitted on the outside of cars convex?

Convex mirrors have the ability to cover wider field of view by forming diminished and virtual image object. Thus, the mirrors fitted on the outside of cars are convex so that larger view of the road can be observed by the drive sitting in the car.

Why does obtaining the image of the sun on paper with help of a concave mirror burn the paper?

The rays from the sun are parallel. When these rays fall on the concave mirror, they are converted to a single point on the focal plane of the mirror. Thus a lot of heat is produced at the point. Now, if a paper is placed at that point to get the image of the sun, the paper gets burnt because of the huge amount of heat concentrated at that point.

Which type of mirrors are used in the following?
Periscope, floodlights, shaving mirror, kaleidoscope, street lights, headlamps of a car.

There are variable types of mirrors used that include flat, concave and convex.
Their usage has been specified as under,-
Periscope – Flat mirror
Floodlights – Concave mirror
Shaving mirror - Concave mirror
Kaleidoscope –Two or more surfaces tilted to each other
Street lights – Convex mirror
Head lamps of a car – Concave mirror

Fill in the blanks:
Light ray enters into water medium from air bends .......... the normal.

Light ray enters into water medium from air bends towards the normal.

A light ray traveling obliquely from a denser medium to a rarer medium bends away from the normal. A light ray bends towards the normal when it travels obliquely from a rarer to a denser medium.

Why is concave lens called diverging lens ?

When the ray of light coming parallel to principle axis after refraction through the concave lens diverges and when we produced these rays backward they appears to meet at a point called focus, since lens diverges the ray of light that is why it is called diverging lens.
1749455_1829330_ans_f495ee3709de4db29dc6a7aef40ec928.png

1749455_1829330_ans_f495ee3709de4db29dc6a7aef40ec928.png

Obtain the position, nature and size of an image formed by a plane mirror from the formula of magnification.

In case of a plane mirror, the magnification, $$m = +1$$
positive magnification indicates that image formed by plane mirror is erect.
As we know, m = Image height/ Object height,
We can say, Image height = Object height.
Therefore, the image formed by a plane mirror is of the same size as the object.
Again we know that,
$$M = - \left( v/u\right)$$
Or, $$v = -u$$
This shows that the image formed by a plane mirror is at the same distance as the object but behind the mirror, i.e. the image formed is virtual.
Hence, we conclude that a virtual and erect image of the same size as that of the object is formed by a plane mirror at the same distance as the object behind the mirror.

Find out the letters of the english alphabet or any other language known to you in which the image formed in a plane mirror appears exactly like the letter itself. Discuss your findings.

A, H, I, M, O, T, U, V, W, and X are the letters. Which form the same image as the letter is. These letters are laterally symmetrical.

How does a light ray travel ?

Light ray travels in a straight line.

Which type of lens forms always a virtual image?

As seen in above ray diagram concave lens always diverge rays after rafraction and hence they never intersect rather they seem to be intersecting at a point when produced backwards hence they always form a virtual image.

1781426_1848048_ans_87441f8b9d484996a8c7ff9c57ac7248.jpg

State the characteristics of the image formed by a plane mirror.

Characteristics of the image formed by a plane mirror are:
1. Virtual and erect.
2. Behind the mirror.
3. Size of the image is equal to the size of the object.
4. Laterally inverted image. (Image of left side visible on the right side)
5. Distance of the image behind the mirror is equal to the distance of an object in front of the mirror.

What is meant by Newtons disc. Explain with neat diagram.

Newton’s colour disc has seven equal parts coloured with rainbow colours. Make a small hole at the centre of the disc. Insert a stick. Ensure that the disc rotates freely. When the disc rotated fast, the colours get mixed together and appears to be whitish.
1781453_1848085_ans_5a891eb5d264402182493704e9dd887c.png

1781453_1848085_ans_5a891eb5d264402182493704e9dd887c.png

Make Newtons disc by painting the constituent colours of white col-our of white light in the same order and proportion.
In which colour does the disc appear when rotated fast?

Very near to the white colour. The Newton disc, also known as the Disappearing Colour Disc, is a well-known physics experiment with a rotating disc with segments in different colors (usually Newton's primary colors: red, orange, yellow, green, blue, indigo, and violet) appearing as white (or off-white or gray) when it spins very fast.

Why it is written on rear-view mirrors that "Objects in the mirror are closer than they appear"?

The image formed by a convex mirror is always erect and diminished. Hence the driver who sees the image of vehicles on the mirror develops a feeling that the vehicles coming from behind are at a greater distance. This may turn out to be dangerous. So that's why this warning is written on them.
1778078_1848220_ans_85f7d56a61bc41c8870ba982b3b8fccf.png

1778078_1848220_ans_85f7d56a61bc41c8870ba982b3b8fccf.png

I. What are the different types of mirror?
II. What are the properties of the images obtained in a face mirror?

$$\large \textbf{Concepts used:}$$

$$\bullet$$ Image formed by plane mirrors

$$\large \textbf{Explanation:}$$

$$\Large \textbf{Part (I)}$$

There are mainly three types of mirrors: two spherical mirrors and one plane mirror.

$$\bullet \ \textbf{Concave mirror}$$

A spherical mirror, whose reflecting surface is curved inwards, that is, faces towards the centre of the sphere.

$$\bullet \ \textbf{Convex mirror}$$

A spherical mirror whose reflecting surface is curved outwards.

$$\bullet \ \textbf{Plane mirror}$$

A smooth, highly polished reflecting plane surface is called a plane mirror.

$$\Large \textbf{Part (II)}$$

Face mirror is a plane mirror. The properties of the images obtained in the plane mirror are:

$$\bullet$$ Image will be formed behind the mirror and will be at equal distance from the mirror as the object.

$$\bullet$$ Image formed is of the same size as the object.

$$\bullet$$ It will be erect and virtual.

$$\bullet$$ Image formed in plane mirror is laterally inverted

Fill in the blanks :
Image obtained on Screen are .............. image.

real

Make Newton’s disc by painting the constituent colors of white color of white light in the same order and proportion. Give Reason.

White light is composed of seven colors.

When a disc painted with seven rainbow colours in equal proportions rotated fast, the colours get mixed together and the disc appears to be whitish. Such a disc is popularly known as Newton’s disc.

When Newton’s colour disc rotates fast it appears white. Which phenomenon is responsible for this?

It is possible due to the persistence of Vision. When an object is viewed by a person, the image remains in the retina for a time interval of $$1/16$$ second. This phenomenon is called persistence of vision.

The disc has seven colours on it. When the disc rotates very fast, the impression of a colour is made on our eyes before the impression of the previous colour fades away. Thus our eyes perceive it as a mixing of all seven colours. Hence it appears white.

1786737_1849302_ans_6c76eb8834d44ef0a5e1eb6abff3ee1d.png

Make Newton’s disc by painting the constituent colours of white colour of white light in the same order and proportion. In which colour does the disc appear when rotated fast?

1786779_1849035_ans_78fcda416c2f4432ab5a1c742468ef0a.jpg

Why the concave lens always create a virtual and erect image of the object?

In this case, refracted Ray does not actually intersect with each other. It appears to intersect the images formed on the same side of the lens.

A student holding a mirror in his hand, directed the reflecting surface of the mirror towards the Sun. He then directed the reflected light on to a sheet of paper held close to the mirror.
Which type of mirror does he have?

Distance from mirror at which ray will converge is called focus.
2159846_1980650_ans_cc99ef05eaac48abbaa6642d944f37fc.jpeg

List differences between real and virtual images.

S. No.	Real Image	Virtual Image
1.	When rays of light after reflection meet at a point, a real image is formed.	When rays of light after reflection do not meet at a point but appears to meet at a point, virtual image is formed.
2.	Real image can be obtained on a screen	Virtual image cannot be obtained on a screen.
3.	Real image is formed in front of a mirror.	Virtual image is formed behind the mirror.
4.	Real image is always inverted.	Virtual image is always erect (i.e., upright)

State three uses of a concave mirror.

Reflector: Concave mirrors are used in motor head lights, search lights and torches etc. to produce an intense parallel beam of light. A bulb is placed at the focus of concave mirror or concave reflecting surface. The beam of light from the bulb after reflecting from the concave mirror goes as a parallel beam (figure 24).

This parallel beam of – light illuminates the road ahead of the vehicle.

Shaving and make up mirror: When an object is placed close to a concave mirror (i.e., between the pole and focus of the concave mirror), an erect and enlarged (large in size) image of the object is formed. Because of this fact, concave mirror is used by men to see their enlarged faces while shaving. Similarly, a lady can see her face better with the help of a concave mirror while doing make up.
In solar cookers: When a parallel beam of sun light falls on a concave mirror, this beam is brought to the focus of the concave mirror. As a result of this, the temperature of an object (say a container containing un-cooked food) placed at this focus increases considerably. Hence the food in the container is cooked (figure 25).

1994821_1951466_ans_fa423ead58bc4fd3af928fc7b3dfbf2f.png

Light travels in a ______ path.

Light travels in a $$\text{straight line}$$ path.

Why do we prefer a convex mirror as a rear- view mirror in vehicles?

Two reasons

(i) It always produced erect and virtual image

(ii) The size of the image is smaller then the object.

Both of the above reason allows the driver to have a wider view of the traffic behind the vehicle in small mirror

Explain the manner in which light travels with the help of an activity.

Take a comb and fix it on one side of a thermacol sheet. Fix a mirror on the other side as shown in figure. Spread a dark coloured sheet of paper between the mirror and the comb, Send a beam of light from a torch through the comb. You get a pattern of light similar to that shown in figure. This activity explains the manner in which light travels and gets reflected from a mirror.

1152519_634750_ans_8f68be522689440faeea5208547a913d.JPG

1152519_634750_ans_8f68be522689440faeea5208547a913d.JPG

Explain an experiment to show the rectilinear propagation of light.

We take three pieces of cardboard. Place them one on the top of one another and make a hole in the middle of each cardboard by using a thick nail. Erect these cards up on the table at a short distance away from each other.

Take a candle which is of the same height as the holes in the cards. Light the candle and place it in front of the cards. We see that the light of the candle is visible only when the holes on cards lie in a straight line.

If we disturb them the light of the candle disappears. This experiment shows that light propagates in a straight line.

At what distance from a convex lens of focal length $$0.15 m $$ must an object be placed so that the image must be twice the size of the object, when the image is
a) real
b) virtual

The magnification is given as

$$m = \frac{{{h_i}}}{{{h_0}}}$$

As it is given that the height of the image is twice that of the object

$$m = 2$$

We know that

$$\frac{{{h_i}}}{{{h_0}}} = - \frac{{{u_i}}}{{{v_0}}} = 2$$

By using the formula

$$\frac{1}{f} = \frac{1}{{{u_0}}} + \frac{1}{{{v_i}}}$$

$$\frac{1}{{15}} = \frac{1}{{{u_0}}} - \frac{1}{{2{u_0}}}$$

Hence for virtual image the distance of the object is $$7.5\;cm$$ and the distance of the image should be $$ - 15\;cm$$

For real image

By using the formula

$$m = - \left( {\frac{{ - {u_i}}}{{{v_0}}}} \right)$$

Hence the distance of the object is $$7.5\;cm$$ and the distance of the image should be $$ - 15\;cm$$

Read the following conversation.
Teacher: "If you want to collect the virtual images, which mirror do you select?".
Bharathi: "convex mirror"
Sowmya: "concave mirror"
Firoz: "plane mirror"
What do you think? Who is correct? Explain.

If we want a virtual image we will require a convex mirror and plane because :

A plane mirror will form an upright virtual image of the object with the same size.

A convex mirror will also form an upright virtual image but will appear smaller. Only a concave mirror can produce a real inverted image whose size depends on screen placement. If the real image and object are the same distance from the concave mirror, then they are both the same size. But if the real image is farther than the object is from the mirror, then the image is larger.

So it follows that if the real image is closer to the mirror than the object then it would be smaller. Also note that there is no real image with a concave mirror if you place the object inside the focal length of the mirror, in which case the image is virtual, upright, and bigger.

Hence, both Bharathi and Firoz are correct.

Give one use each of a concave and a convex mirror.

Concave mirrors : They are used by dentists to see enlarged images of patient’s teeth so that it becomes easier to locate the defect in the tooth.

Convex mirrors : They are used as rear view mirrors in vehicles to see the traffic coming from behind.

Why is convex lens called converging lens ?

When the rays of light coming parallel to principle axis after refraction through the lens passes through a point called focus, since it converge all the ray at one point, that is why it is said to be converging lens.

In which of the following two arrangements (a) and (b) shown in the diagram, you can see the light of the bulb ? Explain Your answer

We can see the light of the bulb in the arrangement (a).
This is so because in arrangement 'a' the rod is straight and light travels in a straight line path.
Whereas in arrangement 'b' the rod is bent. So the light cannot pass through it.
1885033_1906953_ans_f79df362150f4dbd8ea7acce33a8634d.png

1885033_1906953_ans_f79df362150f4dbd8ea7acce33a8634d.png

What is a real image? Name the mirror which can be used to obtain the real image of an object. What should be the position of the object relative to the mirror?

A real image occurs where rays converge.

A concave mirror is capable of producing a real image and this only occurs if the object is located a distance greater than a focal length from the mirror's surface.

1838022_1802944_ans_3bb4460ec930440a87385242e122c0b6.png

Describe an experiment to show that light travels in a straight line path.

Take three cardboards A, B and C each about $$25 cm$$ square. Take a pin and make a small hole in each cardboard at the same height. Suspend the cardboard pieces by separate threads vertically from a support such that each hole is at the same height, as shown. Pass a string through the holes and pull it taut. This makes the three holes in a straight line. Now take out the string.
Place a lighted candle near one of the cardboards (say A). Look at the candle flame from the other side of the cardboard C. The candle flame is clearly seen. Now slightly displace one of the cardboards (say B) so that the holes no longer remain in a straight line. Again look at the candle flame from the other side of the cardboard C. You do not see the candle flame. The reason is that light travels in a straight line and now the holes in the cardboards A, B and C are not in a straight line. Conclusion: Light travels in a straight line path called the rectilinear propagation of light.

A dental doctor uses a mirror of focal length 8 cm. To see the teeth clearly what should be the maximum distance between the teeth and the mirror? Justify your answer. Which type of mirror has been used by the doctor?

The dental doctor uses a concave mirror. Erect , virtual and enlarged image can be obtained using the mirror. Such images are formed when the object is kept in between the main focus and pole of a concave mirror. So the maximum distance between the mirror and the teeth must be in 8 cm to view the teeth clearly.

A small candle, 2.5 cm in size is placed at 27 cm in front of a concave mirror of radius of curvature 36 cm. At what distance from ' the mirror should a screen be placed in order to obtain a sharp image? Describe the nature and size of the image. If the candle is moved closer to the mirror, how would the screen have to be moved?

$$f = \dfrac{R}{2} = - \dfrac{36}{2} = -18 cm$$
$$u = -27 cm$$
size of the object, $$O = 2.5 cm$$
$$\dfrac{1}{u} + \dfrac{1}{v} = \dfrac{1}{f}$$
$$\dfrac{1}{v} = \dfrac{1}{f} - \dfrac{1}{u} = \dfrac{1}{-18} - \dfrac{1}{-27} = - \dfrac{1}{54}$$
$$v = -54 cm$$ (real image)
Therefore, the screen should be placed at a distance of 54cm from the mirror on the same side as the object,
$$\dfrac{I}{O} = \dfrac{-v}{u}$$ or $$\dfrac{I}{2.5} = \dfrac{-54}{-27} = +2$$
$$I = -2 \times 2.5 = -5 cm$$ (inverted image).
When the candle is moved closer to the mirror, the image will move away from the mirror and likewise, the screen has to be moved away to bring the image on the screen. However, when the candle is at a distance less than 18cm, the image formed will be virtual. In that situation, the image cannot be brought to the screen.

How many types of mirror are there? Name them, define them.

There are 3 types of mirrors:

1. Plane mirror: The name itself indicates that this mirror has a plane surface. This type of mirror is used in our homes.

2. Concave mirror: The inner surface of the spherical mirror is reflecting, then it is said to be a concave mirror.

3. Convex mirror: The outer surface of the spherical mirror is reflecting, then it is said to be a convex mirror.

Light - Class 7 Physics - Extra Questions

What is reflection of light?

Name two types of spherical mirrors.

Define Lateral inversion.

State two uses each of : plane mirror

Reflection is the __________ of light off a surface.

Fill in the blanks :A plane mirror forms a ................... and ................... image.

List some characteristics of plane mirror.

Characteristics of the image formed by a plane mirror :

An image that cannot be obtained on a screen is called a________ (real, virtual) image.

Is the image formed by the plane mirror exactly of the same size as the object?

What is a virtual image? Give one situation where a virtual image is formed.

Image obtained on a screen is called _______ image.

What is a mirror ?

What is the difference between virtual images produced by concave, plane and convex mirrors ?

Look at figure. Can the image of the child in it be obtained on a screen? (Yes/No)

For driving a car what type of mirror would you prefer to see traffic at your back andwhy ? (Convex/Concave)

A real image is always .......(inverted/ magnified).

Can a real image be formed with the help of a plane mirror?

Give reasons:Concave mirrors are used in solar devices.

If you stand in front of a big mirror and lift your left hand, which hand will your image in the mirror appear to lift ?

What is the angle, in degrees, between a plane mirror and the straight line joining the object and its image?

State three differences between a real image and virtual image.

Explain why a real image can be projected on a screen but a virtual image cannot.

Show an experiment which proves light always travels in a straight line.

Give the reason for the following: Concave mirrors are used as shaving mirrors.

Write down the letters of the word 'PHYSICS' as seen in a plane mirror held perpendicular to the plane of the paper.

Write three differences between a real image and a virtual image.

State two uses of a convex mirror.

State two uses of a concave mirror.

Boojho stands at A just on the side of a plane mirror as shown in Fig.. Can he see himself in the mirror? Also can he see the image of objects situated at P, Q and R?

Name the type of mirror used in the following situations:a) Headlights of carb) Solar furnaces

State the types of mirrors used for (i) headlights and (ii) rear view mirrors, in cars and motorcycles. Give reason to justify your answer in each case :

When used for its intended purpose, a make-up mirror causes a person's face to look larger and right-side-up. What kind of mirror is a make-up mirror and where should the person be located relative to the focal point (f) to get the desired image?

At an instant, a watch shows time $$2: 35$$ when seen through the mirror, what time will be appeared?

How do you appreaciate the role of spherical mirrors in daily life?

Name equipment where the following are used :a. A concave mirrorb. A convex mirror

Which type of mirror is used in head lights of vehicles?

A plane mirror lying on the ground is not visible from all directions. But a piece of paper can be seen from any direction. Explain.

If a mirror reverses right and left, why does not it reverse up and down?

Why driver prefers to use a convex mirror as rear-view mirror?

Write the differences between convex and concave lens.

Give the uses of a concave mirror.

What is reflection of light? Explain reflection of light with the help of an activity?

How would you define reflection of light?

Draw ray diagrams to show the formation of three times magnified (a) real, and (b) virtual image of an object by a converging lens. Mark the positions of O, F and 2F in each diagram.

Have you ever seen an ambulance? It is written in the form of mirror image on vehicles. Explain why it is done so and give the mirror image of AMBULANCE.

What do we need in order to see a shadow?

State any two differences between Convex and Concave mirrors.

Find out the letters of English alphabet or any other language known to you in which the image formed in a plane mirror appears exactly like the letter itself. Discuss your findings.

If an object is placed at a distance of $$10\ cm$$ in front of a plane mirror, how far would it form its image?

Light travels in .............................. (curved/straight) lines.

What kind of mirror is used in big shopping stores to watch the activities of customers ?

Write down the letters of the word CAPITAL as they appear in a plane mirror held perpendicular to the plane of paper.

A man stands in front of a mirror of a special type.He finds that his image has a very small head,a fat body and legs of normal size.What can be the shapes of the three parts of the mirror?

Define Reflection.

Name the type of mirror used in the following situations.Headlights of a carSide/rear - mirror of a vehicleSolar furnaceSupport your answer with reason

What do you mean by reflection of light?

Write two uses of spherical mirrors.

Draw a ray diagram to show the formation of image of an object placed between the pole and focus of a concave mirror . State the position, size and nature of the image

Write various uses of concave mirror in everyday life

Distinguish between a real and a virtual image of an object. What type of image is formed(i) by a plane mirror, (ii) on a cinema screen ?

What is the important difference between looking at a photograph of your face and looking at yourself in a plane mirror?

What is the difference between a real image and a virtual image? Give one example of each type of image.

A man stands 10 m in front of a large plane mirror. How far must he walk before he is 5 m away from his image?

(a) A boy with a mouth 5 cm wide stand 2 m away from a plane mirror. Where is his image and how wide is the image of his mouth ?(b) The boy walks towards the mirror at a speed of 1 m/s. At what speed does his image approach him?

Name the two types of spherical mirror. What type of mirror is represented by the:(a) back side of a shinning steel spoon?(b) front side of a shinning steel spoon?

What information do we get about sunlight from the formation of a rainbow?

The diagrams show the appearance of a fork when placed in front of and close to two mirrors A and B, turn by turn.(a) Which mirror is convex ?(b) Which mirror is concave ?Give reasons for your choice.

Give two uses of a convex mirror. Explain why you would choose convex mirror for these uses.

What type of mirror could be used as a dentist's mirror ?

Where in nature can you find evidence that white sunlight may be made of different colours?

Name the scientist who discovered that sunlight consists of seven colours.

What type of mirror could be used :(a) as a shaving mirror ?(b) as a shop security mirror ?

A man sits in an optician's chair, looking into a plane mirror which is 2m away from him and views the image of a chart which faces the mirror and is 50cm behind his head. How far away from his eyes does the chart appear to be?

A person wants to see the full-length image of a tall building in a small mirror. Which type of mirror should be used by him?

What is the distance between the image and the plane mirror, if the object is at $$15\ m$$?

Write one use of such mirror images on a daily basis. Write STOP as it should written on the front of a police car.

List two characteristics of the images formed by plane mirrors?

What type of image is formed on a cinema screen?

Fill in the blanks :
A plane mirror forms a ................... and ................... image.

For driving a car what type of mirror would you prefer to see traffic at your back and
why ? (Convex/Concave)

Give reasons:
Concave mirrors are used in solar devices.

Name the type of mirror used in the following situations:
a) Headlights of car
b) Solar furnaces

Name equipment where the following are used :
a. A concave mirror
b. A convex mirror

Name the type of mirror used in the following situations.
Headlights of a car
Side/rear - mirror of a vehicle
Solar furnace
Support your answer with reason

Distinguish between a real and a virtual image of an object. What type of image is formed
(i) by a plane mirror, (ii) on a cinema screen ?

(a) A boy with a mouth 5 cm wide stand 2 m away from a plane mirror. Where is his image and how wide is the image of his mouth ?
(b) The boy walks towards the mirror at a speed of 1 m/s. At what speed does his image approach him?

Name the two types of spherical mirror. What type of mirror is represented by the:
(a) back side of a shinning steel spoon?
(b) front side of a shinning steel spoon?

The diagrams show the appearance of a fork when placed in front of and close to two mirrors A and B, turn by turn.
(a) Which mirror is convex ?
(b) Which mirror is concave ?
Give reasons for your choice.

What type of mirror could be used :
(a) as a shaving mirror ?
(b) as a shop security mirror ?

Fill in the blanks:
A plane mirror _______ reflect 100 percent light falling on it.

Fill in the blanks:
The image formed by a plane mirror is erect and ______.

Answer the following question.
Why are the mirrors fitted on the outside of cars convex?

Which type of mirrors are used in the following?
Periscope, floodlights, shaving mirror, kaleidoscope, street lights, headlamps of a car.

Fill in the blanks:
Light ray enters into water medium from air bends .......... the normal.

Make Newtons disc by painting the constituent colours of white col-our of white light in the same order and proportion.
In which colour does the disc appear when rotated fast?

I. What are the different types of mirror?
II. What are the properties of the images obtained in a face mirror?

Fill in the blanks :
Image obtained on Screen are .............. image.

A student holding a mirror in his hand, directed the reflecting surface of the mirror towards the Sun. He then directed the reflected light on to a sheet of paper held close to the mirror.
Which type of mirror does he have?

At what distance from a convex lens of focal length $$0.15 m $$ must an object be placed so that the image must be twice the size of the object, when the image is
a) real
b) virtual

Read the following conversation.
Teacher: "If you want to collect the virtual images, which mirror do you select?".
Bharathi: "convex mirror"
Sowmya: "concave mirror"
Firoz: "plane mirror"
What do you think? Who is correct? Explain.