MCQ Questions for Class 10 Physics Light Reflection And Refraction Quiz 12

The radius of curvature of a concave mirror is

$40\ cm$ and the size of the real image is twice as that of an object, then the object distance is:

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$60\ cm$
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$20\ cm$
0%
$40\ cm$
0%
$30\ cm$

Explanation

Given, Concave mirror

Radius of curvature,

$R = -40\ cm$
Magnification,

$m = -2$ (for real image

$m$ is negative)

Focal length,

$f = \dfrac{R}{2} = \dfrac{-40}{2} = -20\ cm$

We know,

$m = \dfrac{-v}{u}$

$-2 = \dfrac{-v}{u}$

$\Rightarrow u = \dfrac{v}{2}$

$\Rightarrow v = 2u$

Using mirror formula,

$\dfrac{1}{f} = \dfrac{1}{v} + \dfrac{1}{u}$

$\Rightarrow \dfrac{1}{-20} = \dfrac{1}{2u} + \dfrac{1}{u} = \dfrac{3}{2u}$

$\Rightarrow 2u = 3 \times (-20)$

$u = \dfrac{-60}{2} = -30\ cm$

$u = -30\ cm$

The object is

$30\ cm$ from the mirror.

The ratio of thickness of plates of two transparent medium

$A$ and

$B$ is

$6:4$ . If the takes equal time in passing through them, then refractive index of

$B$ with respect to

$A$ will be

0%
$1.4$
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$1.5$
0%
$1.75$
0%
$1.33$

Explanation

Time taken by light to travel distance

$x$ through a medium of refractive index

$\mu$ is

$t=\dfrac {\mu x}{c}\Rightarrow \dfrac {\mu_B}{\mu_A}=\dfrac {x_A}{x_B}=\dfrac {6}{4}\Rightarrow _A\mu_B =\dfrac {3}{2}=1.5$

The time required to pass the light through a glass slab of

$2\ mm$ thick is

$(\mu_{glass}=1.5)$

0%
$10^{-5}s$
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$10^{-11}s$
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$10^{-9}s$
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$10^{-13}s$

Explanation

As we know,

$t=\dfrac {\mu x}{c}=\dfrac {1.5\times 2\times 10^{-3}}{3\times 10^8}=10^{-11} sec$

An object

$1\ cm$ tall is placed

$4\ cm$ infront of a mirror. In order to produce an upright image of

$3\ cm$ height one needs a

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Convex mirror of radius of curvature $12\ cm$
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Concave mirror of radius of curvature $12\ cm$
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Concave mirror of radius of curvature $4\ cm$
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Plane mirror of height $12\ cm$

Explanation

Erect and enlarged image can be produced by a concave mirror.

From the definition of magnification we get,

$m=\dfrac{\text{Height of the image}}{\text{Height of the object}}=+\dfrac{3}{1}=+3$

We also know that

$m=-\dfrac{v}{u}=+3$

$\Rightarrow v=-3u=-3\times (-4)=12\ cm$

Using mirror formula we get

$\dfrac{1}{v}+\dfrac{1}{u}=\dfrac{1}{f}$

$\therefore \dfrac{1}{12}+\dfrac{1}{-4}=\dfrac{1}{f}$

$\Rightarrow \dfrac{1-3}{12}=\dfrac{1}{f}$

$\Rightarrow f=-6\ cm$

The radius of curvature of the mirror is

$R=2f=2\times 6 = 12\ cm$ , and it is a concave mirror as the focal length is -ve.

Which of the following ray diagram show physically possible refraction

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(i)
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(ii)
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(iii)
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None of these

Explanation

When light ray goes from denser to rarer medium (i.e. more

$\mu$ to less

$\mu$ ) it deviates away from the normal

On the other hand, if light ray goes from rarer to denser medium (i.e. less

$\mu$ to more

$\mu$ ) it bends towards the normal.

It is followed only in option A.

In option B, the refracted ray is on the same side of the normal as the incident ray, which never happens in case of any refraction. So it is incorrect.

What is the time taken

$(in\ s)$ to cross a glass of thickness

$4\ mm$ and

$\mu=3$ by light?

0%
$4\times 10^{-11}\ s$
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$2\times 10^{-11}\ s$
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$16\times 10^{-11}\ s$
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$8\times 10^{-10}\ s$

Explanation

Thickness of the glass,

$d = 4\ mm = 4 \times 10^{-3}\ m$
Refractive index of the glass

$\mu = 3$
We know

$\mu = \dfrac{\text{Speed of light in vacuum}}{\text{Speed of light in glass}} = \dfrac{c}{v}$

$3 = \dfrac{3 \times 10^{8}}{v}$

$\Rightarrow v = 1 \times 10^{8}\ m/s$

$\text{Speed} = \dfrac{\text{distance}}{\text{time}}$

$\Rightarrow \text{time} = \dfrac{\text{distance}}{\text{speed}} = \dfrac{4 \times 10^{-3}\ m}{1 \times 10^{8}\ m/s}$

$\text{time}, t = 4 \times 10^{-11}\ s$

A convex mirror has a focal length

$f.$ A real object is placed at a distance

$f$ in front of it from the pole produces an image at

0%
Infinity
0%
$f$
0%
$f/2$
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$2f$

Explanation

Here focal length

$=f$ and

$u=-f$
On putting these values in

$\dfrac{1}{f}=\dfrac{1}{u}+\dfrac{1}{v}$

$\Rightarrow \dfrac{1}{f}=-\dfrac{1}{f}+\dfrac{1}{v}\Rightarrow v=\dfrac{f}{2}$

Match List

$I$ with List

$II$ and select the correct answer using the codes given below the lists:

List $I$	List $II$
(Position of the object)	(Magnification)
(I) An object is placed at focus before a convex mirror	(A) Magnification is $- \infty$
(II)An object is placed at centre or curvature before a concave mirror	(B) Magnification is $0.5$
(III) An object is placed at focus before a concave mirror	(C) Magnification is $+1$
(IV) An object is placed at centre or curvature before a convex mirror	(D) Magnification is $-1$
	(E) Magnification is $0.33$

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$I-B, II-D, III-A, IV-E$
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$I-A, II-D, III-C, IV-B$
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$I-C, II-B, III-A, IV-E$
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$I-B, II-E, III-D, IV-C$

A medium shows the relation between the angle of incidence

$i$ and the angle of refraction

$r$ . If speed of light in the medium is

$nc$ then value of

$n$ is

0%
$1.5$
0%
$2$
0%
$2^{-1}$
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$3^{-1/2}$

Explanation

Let

$\mu$ be the refractive index of the medium.

From Snell's law:

$\mu=\dfrac{sin\ i}{sin\ r}$

From graph it is clear that

$\tan 30^{o}=\dfrac{\sin r}{\sin i}$

$\Rightarrow \dfrac{1}{\sqrt{3}}=\dfrac{\sin r}{\sin i}=\dfrac{1}{\mu}\Rightarrow \mu=\sqrt{3}$
Also, speed of light in the medium

$v=\dfrac{c}{\mu}=nc\Rightarrow n=\dfrac{1}{\mu}=\dfrac{1}{\sqrt{3}}=(3)^{-1/2}$

A concave mirror of focal length

$15\ cm$ forms an image having twice the linear dimensions of the object. The position of the object when the image is virtual will be

0%
$22.5\ cm$
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$7.5\ cm$
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$30\ cm$
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$45\ cm$

Explanation

Given,

$f=-15\ cm$ ; focal length

$m=\pm 2$ ; magnification(Positive because image is virtual)
We know that-

$\Rightarrow m=-\dfrac{v}{u}$

$\Rightarrow v=-2u.$

By using mirror formula-

$\dfrac{1}{f}=\dfrac{1}{v}+\dfrac{1}{u}$

$\Rightarrow \dfrac{1}{-15}=\dfrac{1}{(-2u)}+\dfrac{1}{u}$

$\Rightarrow u=-7.5\ cm$

The absolute refractive indices of water glass and diamond are 1.77, 1.50, and 2.72 respectively, which medium is most optically denser?

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Water
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Glass
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Diamond
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None

A light ray containing both blue and red wavelengths is incident at an angle on a slab of glass. Which of the sketches in this fig represents the most likely outcome?

0%
$A$
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$B$
0%
$C$
0%
$D$
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None of them

Explanation

Answer (c). For any medium, other than vacuum, the index of refraction for red light is slightly lower (closer to 1 ) than that for blue light. This means that when light goes from vacuum (or air) into glass, the red light deviates from its original direction less than does the blue light. Also, as the light reemerges from the glass into vacuum (or air), the red light again deviates less than the blue light. If the two surfaces of the glass are parallel to each other, the red and blue rays will emerge traveling parallel to each other, but displaced laterally from one another. The sketch that best illustrates this process is

$C$ .

Where can we see an image formed the lens of an object?

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On the object itself
0%
On the lens itself
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On the same side of the object
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On the opposite side of the object

Explanation

The image formed by a lens is on the
side opposite to that of the object, thus option

$D$ is correct.

Choose whether true or false:-
The lenses which feel thicker in the middle than at the edges are converging lenses.

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True
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False

Which of the following are the properties of lenses?

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Opaque
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Transparent
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Allows light to pass through
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Shiny

Why is convex lens used as a magnifying glass?

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It forms erect image
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It forms real image
0%
It forms virtual image
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It forms magnified image

What does the distance PF denote?

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Focus
0%
Focal Plane
0%
Centre of curvature
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Focal length

Explanation

The point on the principal axis from which all the light rays which are parallel to the principal axis appear to diverge after reflection from the convex mirror is known as the focus of the convex mirror.

The distance between the pole

$P$ and focus

$F$ is called the focal length.

Principal focus is represented by

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R
0%
f
0%
P
0%
F

In a convex mirror, the reflected moves parallel to the principal axis ray appear to come from a point on the principal axis.

0%
True
0%
False

A number of rays parallel to the principal axis falling on a concave mirror intersect at a point, called the principal focus.

0%
True
0%
False

For concave mirror, the focus is in ________ of the mirror.

0%
behind
0%
front
0%
above
0%
below

For convex mirror, the focus is _______ the mirror.

0%
behind
0%
front
0%
above
0%
below

Explanation

For convex mirror, the focus is behind the mirror.

$F$ is focus in the diagram

2000529_1953300_ans_526f29aca35e48ef9147551674022263.png

The plane through the focus perpendicular to the axis of a mirror or lens is

0%
Focal length
0%
Focus
0%
Focal Plane
0%
Pole

An object 4 cm in size, is placed at 20 cm in front of a concave mirror
of focal length 15 cm. Which of the following correctly represents the object distance (u) and focal length (f), as per New Cartesian sign
convention?

0%
$u= 20 cm, f =-15cm$
0%
$u=-20 cm, f =-15cm$
0%
$u=20 cm, f =15cm$
0%
$u=-20 cm, f =15cm$

Explanation

Since object distance is kept in front of the concave mirror, it is taken to be negative. The focal length of the concave mirror is taken as negative.
Hence

$u=-20 cm, f =-15cm$

All the distances measured to the left of the origin are taken as _________.

0%
zero
0%
positive
0%
one
0%
negative

Distances measured perpendicular to and above the principal axis are taken as ________.

0%
negative
0%
positive
0%
zero
0%
none of the above

All the distances measured to the ________ of the origin are taken as positive.

0%
left
0%
below
0%
right
0%
None of the above

In the case of a convex mirror, the image distance is taken to be positive because:

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Image is formed in front of the mirror
0%
centre of curvature and focus lies behind the convex mirror
0%
Image is always formed behind the mirror
0%
None of these

A spherical mirror has focal length -10cm. What type of mirror is it likely to be?

0%
convex
0%
concave
0%
plane
0%
none of the above

In case of spherical mirrors, object distance is taken to be_______

0%
positive
0%
negative
0%
unity
0%
zero

Distances measured perpendicular to and below the principal axis are taken as ________.

0%
negative
0%
positive
0%
zero
0%
one

All distances parallel to the principal axis are measured from the centre of curvature of the mirror.

0%
True
0%
False

In case of lenses. Image distance is negative for _______.

0%
real image
0%
virtual image
0%
mirror image
0%
none of the above

In lenses, all the distances measured to the ________ of the origin are taken as positive.

0%
Left
0%
Right
0%
Below
0%
None of the above

Sign conventions for lenses and mirrors are different.

0%
True
0%
False

Explanation

Sign conventions for lenses and mirrors are not different.

The principal axis of the mirror is taken as the

$x-axis$ of the coordinate system. The conventions are as follows:

$(i)$ The object is always placed to the left of the mirror. This implies that the light from the object falls on the mirror from the left-hand side.

$(ii)$ All distances parallel to the principal axis are measured from the pole of the mirror.

$(iii)$ All the distances measured to the right of the origin (along

$+ x-axis$ ) are taken as positive while those measured to the left of the origin (along

$– x-axis$ ) are taken as negative.

$(iv)$ Distances measured perpendicular to and above the principal axis (along

$+ y-axis$ ) are taken as positive.

$(v)$ Distances measured perpendicular to and below the principal axis (along

$–y-axis$ ) are taken as negative.

Distances measured perpendicular to and below the optical center are taken as ________.

0%
Zero
0%
Negative
0%
Positive
0%
None of the above

Focal length of concave lens is ________.

0%
positive
0%
negative
0%
zero
0%
none of the above

Distances measured perpendicular to and above the optical center are taken as ________.

0%
Negative
0%
Positive
0%
Zero
0%
None of the above

Focal length of convex lens is _________

0%
Negative
0%
Zero
0%
Unity
0%
Positive

For a lens, the image distance is positive for _____.

0%
Real image
0%
Virtual image
0%
Plane image
0%
None of these

Explanation

For a lens, the image distance is positive for a real image.

All distances parallel to the principal axis are measured from the pole of the mirror. All the distances measured to the right of the origin (along

$+ x-axis$ ) are taken as positive while those measured to the left of the origin (along

$– x-axis$ ) are taken as negative.
2112479_1954312_ans_4b6e29f0bd5a4fe5839c755da2fd8661.png

In lenses, the distances measured to the left of the origin are taken as _________.

0%
Zero
0%
One
0%
Positive
0%
Negative

A lens has focal length of -30 cm . Identify the lens.

0%
Convex
0%
Cylindrical
0%
Concave
0%
None of the above

If a man's face is 25 cm in front of concave having mirror producing erect image 1.5 times the size of face, focal length of the mirror would be

0%
75 cm
0%
25 cm
0%
15 cm
0%
60 cm

A lens has focal length of

$+20 cm$ . Identify the lens.

0%
Convex
0%
Concave
0%
Cylindrical
0%
None of the above

In case of lenses, object distance is taken to be_______.

0%
Positive
0%
Zero
0%
Negative
0%
One

CBSE Questions for Class 10 Physics Light Reflection And Refraction Quiz 12 - MCQExams.com

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Practice Class 10 Physics Quiz Questions and Answers

CBSE Questions for Class 10 Physics Light Reflection And Refraction Quiz 12 - MCQExams.com

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Practice Class 10 Physics Quiz Questions and Answers

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