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CBSE Questions for Class 12 Medical Physics Electromagnetic Waves Quiz 3 - MCQExams.com
CBSE
Class 12 Medical Physics
Electromagnetic Waves
Quiz 3
The wavelength of light visible to eye is of the order of
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$$10^{-4}m$$
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$$10^{-8}m$$
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$$10^{-10}m$$
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$$10^{-7}m$$
Explanation
Visible light which is detectable by the human eye - consists of wavelengths ranging from approximately $$780 \ nano \ meter (7.80 \times 10^{-7} m) $$ down to $$390 \ nano \ meter (3.90 \times 10^{-7} m$$). So, the wavelength of light visible to eye is of the order of $$10^{-7}$$m.
According to Maxwell's hypothesis, changing of electric field give rise to
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Magnetic field
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Pressure gradient
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Charge
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Voltage
Explanation
Changing of electric field produces displacement current which produces magnetic field. So, changing electric field
produces magnetic field.
_________ are useful in studying the
structures of
crystals.
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All electromagnetic radiations
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Light rays
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X-rays
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$$\gamma$$-rays
Explanation
X-rays are useful in studying the
structures of
crystals
Why does radio reception improve slightly during the night ?
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The outside noise is reduced very much at night.
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Unlike the daytime, only a few radio stations broadcast during the night.
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Sunlight affects radio broadcasts to some extent during the day.
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The magnetic field of the earth acts with reduced intensity during the night, thereby reducing its impact on broadcasts.
Explanation
Answer is C.
The D region is the lowest of the regions within the ionosphere that affects radio communications signals to any degree. It is present at altitudes between about 60 and 90 kilometers and the radiation within it is only present during the day to an extent that affects radio waves noticeably. It is sustained by the radiation from the Sun and levels of ionization fall rapidly at dusk when the source of radiation is removed. It mainly has the affect of absorbing or attenuating radio communications signals particularly in the LF and MF portions of the radio spectrum, its affect reducing with frequency. At night it has little effect on most radio communications signals although there is still a sufficient level of ionization for it to refract VLF signals.
Hence, radio reception improve slightly during the night because, sunlight affects radio broadcasts to some extent during the day.
Who first proposed the light as an electromagnetic wave ?
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Thomas Young
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Max planck
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James Clerk Maxwell
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Albert Einstein
Explanation
In 1864, Maxwell predicted the existence of electromagnetic waves, the existence of which had not been confirmed before that time, and out of his prediction came the concept of light being a wave, or more specifically, a type of electromagnetic wave.
It is a wide intuition that Albert Einstein proposed the dual nature theory but is not correct.
The increasing order of frequencies for infrared rays, Ultraviolet rays-, X-rays and Y-rays will be-
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y-rays, X-rays, Infrared rays, Ulterviolet rays
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X-rays,Y-rays Infrared rays,Ultraviolet rays
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Infrared rays, Ultraviolet rays,X-rays, Y-rays
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Ultraviolet rays,X-rays, Y-rays Infrared rays
Explanation
The following are the frequencies ranges
for IF, U.V, X-rays and Y-rays
If rays $$ -3\times 10^{11}h_{2} $$ $$ 4\times 10^{4}h_{2} $$
UV rays $$ -7\times 10^{14}h_{2}-1.5\times 10^{15}h_{2} $$
x-rays $$ - 3\times 10^{10}h_{2}-3\times 10^{19}h_{2} $$
r - rays $$ - 3\times 10^{19}h_{2}-73\times 10^{19}h_{2} $$
Option $$-C $$ is correct
_______ is the characteristic of colour
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Wavelength
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Frequency
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Speed
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None of the above
Explanation
Wavelength is the characteristic of colour.
EM waves are
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deflected by electric and magnetic waves
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not deflected by electric and magnetic waves
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sometimes deflected sometimes not deflected
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none of the above
Explanation
EM waves are not deflected by electric and magnetic field. They exhibit the property of reflection and refraction.
The portion of the spectrum beyond the red end is called
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UV spectrum
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Infrard spectrum
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Microwave
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All
Explanation
The portion of spectrum just beyond the red end is called infrared spectrum, while the portion of the spectrum just before the voilet end is called the ultravoilet spectrum.
Most energetic radiations and fluorescence are properties of
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Gamma rays
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UV Rays
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Infrared Rays
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Radio waves
Explanation
Gamma Rays are most energetic Radiations. Since they have high penetrating power, they can cause fluorescence on fluorescent materials like ZnS.
Gamma rays have frequency(f)
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$$f > 3 \times 10^{19} Hz$$
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$$7.5 \times 10^{14}Hz < f < 3 \times 10^{16} Hz$$
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$$<3 \times 10^7 Hz$$
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None of the above
Explanation
Frequency of gamma rays is greater than $$3 \times 10^{19} Hz$$
When an object absorb waves and energy their temperature increases.
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True
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False
Explanation
Warm object normally give off infrared but if they become really hot they start emitting light.
If $$c$$ is the speed, $$\nu$$ is frequency and $$\displaystyle \lambda $$ is wavelength of EM waves, then
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$$\displaystyle c=\nu\lambda $$
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$$\displaystyle \frac { \lambda }{ \nu } =c$$
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$$\displaystyle \frac { \nu }{ \lambda } =c$$
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$$\displaystyle \frac { 1 }{ \lambda } =\frac { c }{ \nu} $$
Explanation
$$\displaystyle c=\nu \lambda $$
$$c=$$speed
$$\nu=$$Frequency
$$\displaystyle \lambda $$ = wavelength
EM waves travels with a speed of
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260m/s
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$$\displaystyle 3\times { 10 }^{ 8 }m/s$$
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$$\displaystyle 22\times { 10 }^{ 18 }m/s$$
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2m/s
Explanation
EM waves travel with the same speed in vacuum (or air) which is same as the speed of light ie. $$\displaystyle 3\times { 10 }^{ 8 }m/s$$
On changing of medium, ______ remains same.
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Wavelength
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Frequecy
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Speed
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None
Explanation
Frequency remains same on change of medium, wavelength and speed changes.
How can Infrared radiations be harmful for humans
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Can cause blindness
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Can cause skin burns
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Can cause hairfall
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Can cause frostbite
Explanation
Infrared radiations are carriers of heat and excessive exposure can cause skin burns.
Which of the following is absorbed by the ozone layer ?
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only gamma rays
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visible light
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radio waves
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ultraviolet
Explanation
Ozone is a molecule made of three oxygen atom or $$O_3$$. When ultraviolet light in the range $$240nm$$ and $$320 nm$$ strikes an ozone molecule, it absorbs the energy and the $$O_3$$ changes to $$O_2$$ and $$O$$. The $$O$$ atom soon combines with another $$O_2$$ molecule to form $$O_3$$ and is ready to absorb ultra violet light.
Electromagnetic waves exhibit the property of
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Reflection
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Refraction
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Total internal reflection
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Both A and B
Explanation
EM waves exhibit the properties of reflection and refraction. In refraction, when an EM wave passes from one medium to the another, its direction to travel,speed and wavelength changes, but frequency remains unchanged.
Where are radiowaves used?
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Radar, radio and tv communications
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Microwave ovens
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Photographic films
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sterilizing purpose
Explanation
Radiowaves are used in-
1. Radar communications
2. Radio and TV communications
Electromagnetic theory suggests that the light consists of:
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Magnetic vector only
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Electric vector only
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Electric and magnetic vectors perpendicular to each other
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Parallel electric and magnetic vector
Explanation
Electromagnetic theory suggests that light is a vibration of electric field and magnetic field vectors mutually perpendicular to each other and both being perpendicular to the direction of propagation of electromagnetic wave.
Which of the following are use of microwaves?
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They are used for satellite communication.
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They are used for analysis of atomic and molecular structure.
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They are used cooking in microwave ovens.
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All of the above.
Explanation
Microwaves are used in the following applications:
1. Satellite communications
2. Radar communications
3. Analysis of atomic and molecular structure
4. Cooking in microwave ovens
What are the harmful effects of ultraviolet radiations?
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It can cause skin cancer.
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It contributes to global warming.
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It contributes to greenhouse effect.
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It can cause depletion of natural resources.
Explanation
Long exposure to ultraviolet radiations can cause health hazards like skin cancer.
The electromagnetic waves travel in free space with the velocity of
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Sound
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Light
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Greater than that of light
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Greater than that of sound
Explanation
Electromagnetic waves travel in free space or vacuum with the velocity of light, $$c= 3 \times 10^8\:m/s$$.
Choose the correct answer from the alternatives given.
Which of the following electromagnetic waves have the smallest wavelength?
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$$\gamma$$-rays
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$$X$$-rays
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UV waves
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Infrared rays
Explanation
All electromagnetic waves travel at the same speed.
Speed $$=$$ wavelength $$\times$$ frequency.
Since frequency of $$\gamma$$ rays is the largest, their wavelength must be the smallest.
Which of the following is not an electromagnetic wave?
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Light rays
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X-rays
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Alpha rays
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Gamma rays
Explanation
$$\alpha$$ rays are doubly charged He
i.e. Helium nuclei which are not electromagnetic waves. Others belong to electromagnetic spectrum having different wavelengths.
Which of the following types of waves travels at the greatest speed through the vacuum?
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Radio waves
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Microwaves
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Ultraviolet light
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$$X$$-rays
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None of the above; all these waves would travel at the same speed
Explanation
Since the speed of any types of wave in vacuum remains constant so all wave travel at the same speed.
Infrared radiation was discovered in $$1800$$ by.
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William Wollaston
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William Herschel
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Wilhelm Roentgen
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Thomas Young
Explanation
Infrared radiation was discovered in $$1800$$ by $$William Herschel$$.
They discovered $$\longrightarrow $$ When sunlight went through various color filters; it produces different amount of heat. He hypothesized that colors could have different temperatures. He then passed light through glass prism, creating a color spectrum and analysing each color's temperature. He used three special thermometers.
For each color, one was placed within its bounds while the other two were outside as controls. The thermometer in the color had higher temperature than the others, and he found that each color going from violet to red was warmer than the last. He then placed a thermometer next to red light, where no color from spectrum were visible. He noticed that area had even higher temperature than color sections. He demonstrated that this visible type of light refracted and reflected the same way sunlight did.This light came to be known as infrared radiation.
Electromagnetic waves of wavelength ranging from $$100\mathring{A}$$ to $$\mathring{A}$$ comes under
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X-rays
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UV regions
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Visible region
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Infrared region
Explanation
X-rays: $$10 nm-10 pm\ i.e.\ 10^{-8}m-10^{-11}m$$
Given frequency range: $$100 \mathring A- 1 \mathring A\ i.e.\ 10^{-8}m-10^{-10}m$$
Hence, given wavelength range falls under X-rays
The electromagnetic wave travel in free space with the velocity of
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Sound
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Light
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Greater than that of light
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Greater than that of sound
Explanation
Electromagnetic waves travel at the speed of light ($$3 \times 10^8\ m/s$$) in vacuum.
In electromagnetic wave, according to Maxwell, changing electric field gives _______.
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stationary magnetic field
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conduction current
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eddy current
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displacement current
Explanation
By integral form of modified Maxwell's equations, we have:
$$\oint _{ \partial S } { B }\cdot d{ \ell }=\mu _{ 0 }\int _{ S } ({ J }+\epsilon _{ 0 }\dfrac { \partial { E } }{ \partial t } )\cdot d{ S }\, $$
Where the displacement current density is given by:
$${ J }_{ D }={ \epsilon }_{ 0 }\dfrac { \partial E }{ \partial t } $$
The above integral states that, the line integral of magnetic field around any loop is equal to $${ \mu }_{ 0 }$$ times the surface integral of the total current density (free current plus displacement current) over any open surface which has the loop as its boundary.
Thus, it is clearly seen that a changing electric field gives rise to displacement current.
Electromagnetic theory suggests that the light consists of
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Magnetic vector only
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Electric vector only
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Electric and magnetic vector perpendicular to each other
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Perpendicular electric and magnetic vector
Explanation
Classically, electromagnetic radiation consists of electromagnetic waves
, which are synchronized oscillations
of perpendicular electric
and magnetic fields
that propagate at the speed of light
through vacuum.
Which of the following light has the combination of all frequencies of visible light ?
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white light
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black light
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ultraviolet light
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infrared light
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transparency
Explanation
The visible light contains 7 colours : Violet, indigo, Blue, Green, Yellow, Orange and Red.
White colour is formed by the interference of all 7 colours, thus white light has the combination of all frequencies of visible light.
Identify most suitable options for the following vacant space. The visible light spectrum sits between the _____and _______regions of the electromagnetic spectrum.
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infrared; ultraviolet
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infrared; X-ray
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infrared; gamma ray
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microwave; ultraviolet
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radio; ultraviolet
Explanation
From the electromagnetic spectrum shown above, it is clear that the visible region lies in between infrared and ultraviolet region.
According to the electromagnetic spectrum, As the frequencies of the pure spectral colours increase, the wavelengths of the colours:
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decrease
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increase
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remain the same
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decrease by a factor of 2
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increase by a factor of 2
Explanation
Speed of all the electromagnetic waves is constant and is equal to speed of light i.e $$c$$
Using $$\lambda \times \nu = c = constant$$
$$\implies$$ If frequencies of the pure spectral colours increase then their wavelength will decrease.
According to the electromagnetic spectrum. Which of the following is NOT a pure spectral colour?
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white
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violet
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red
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blue
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yellow
Explanation
Electromagnetic spectrum of visible light : $$VIBGYOR$$
VIBGYOR stands for Violet, Indigo, Blue, Green, Yellow, Orange and Red.
These are pure spectral colours but not white. Infact, white colour is formed due to interference of all these 7 colours.
Identify which of the following is NOT a characteristic of electromagnetic waves?
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contain electrical properties
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have crests and troughs
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contain magnetic properties
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travel through space
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have crests but no troughs
Explanation
Electromagnetic waves (EM) have sinusoidal electrical as well as magnetic waves at right angle to each other and the EM waves propagate through the space with a speed equal to speed of light.
Also the EM waves have both crests and troughs.
Identify t
he waves with the largest wavelengths .
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Radio
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Gamma Rays
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X-Rays
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Visible Light
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Infrared Radiation
Explanation
Order of wavelength from smallest to largest :
Gamma rays < X-rays < Visible light < Infrared Radiation < Microwaves < Radio waves
Thus radio waves has the largest wavelength.
According to the electromagnetic spectrum, radio waves have the ______frequency and the __________ wavelength.
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lowest; largest
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lowest; smallest
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highest; smallest
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highest; largest
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medium; medium
Explanation
Radio waves are the least energetic waves among other waves. They have the lowest frequency and thus the largest wavelength. Due to this large wavelength character, the radio waves are used in data transmission purposes, since they are hard to interact with particles in the atmosphere.
Fill the most suitable option. Mosquitoes and some snakes find their food using vision in the ___ range.
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infrared
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ultraviolet
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radio
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microwave
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visible light
Explanation
Infrared light has longer wavelengths and lower energy than visible light and cannot be seen with the human eye. Mosquitoes,
vampire bats, bed bugs, and some snake a
nd beetle species, however, can use portions of the infrared
spectrum for vision
. Sometimes humans can “see" infrared
energy in the form of heat.
Of the following waves has the longest wavelength?
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X-rays
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Green light
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Orange light
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Microwaves
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Gamma rays
Explanation
Order of wavelength from shortest to longest :
Gamma rays < X-rays < Green light < Orange light < Microwaves
Thus Microwaves has the longest wavelength.
If a particular electromagnetic wave has the highest frequencies among the other electromagnetic waves then it should have the smallest
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wavelengths
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speeds
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amplitudes
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energies
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periods
Explanation
Electromagnetic waves travel with constant speed equal to that of light i.e $$v =c= constant$$
For EM waves $$\lambda \times \nu = c =$$ constant
Thus waves with highest frequency will have smallest wavelength.
In an electromagnetic spectrum, identify which of the following lists are ordered from longest wavelength to shortest wavelength?
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X ray, ultraviolet, visible light
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visible light, ultraviolet , X-ray
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ultraviolet, X-ray, visible light
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ultraviolet, visible light, X-ray
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X-ray, visible light, ultraviolet
Explanation
Decreasing order of wavelength :
Visible light > ultraviolet > X-ray
Thus option B is correct.
In photocell cesium, coated oxidized silver cathode emits electrons for
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visible light.
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ultraviolet.
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infrared light.
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x-rays.
Explanation
In photocell cesium, coated oxidised silver cathode emits electrons for infrared light.
Identify which of the following is NOT a source of visible light?
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red-hot metal
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cool metal
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fluorescent bulb
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the Sun
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fire
Explanation
When the electrons in the atom are excited, for example by being heated, the additional energy pushes the electrons to higher energy orbits. When the electrons fall back down and leave the excited state, energy is re-emitted in the form of a photon.
Thus the hot objects release photons that have energies lying in the visible region. However photons from cool metal do not have energy enough to lie in visible region.
Which of the following colors of light has the lowest frequency?
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Yellow
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Violet
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Orange
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Blue
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Green
Explanation
The color with the lowest frequency corresponds to the longest wavelength, which is orange in this case.
Maxwell introduced displacement current to remove the conceptual contradiction in
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Gauss's law in electrostatics
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Gauss's law in magnetism
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Faraday's law
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Ampere's law
Explanation
Maxwell pointed out the inconsistency of the Ampere's circuital law, when this law was applied to an electric circuit having a capacitor, the law appeared wrong or incomplete. Because no current was assumed in the space between the plates of capacitor. Maxwell said that there is also a current flow, in the space between the plates of a capacitor due to time varying electric field between the plates. Maxwell named this current as displacement current ($$i_{d}$$). This concept makes a continuous flow of current in an electric circuit containing a capacitor.
Now the improved Ampere's law, called Ampere-Maxwell's law is given by:
$$\oint\vec B.\vec dl=\mu_{0}i_{c}+\mu_{0}\varepsilon_{0}\dfrac{d\phi_{E}}{dt}$$
Maxwell's corrections to Ampere's law was required when the later was extended to:
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a static situation
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a non-static situation
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a semi-static situation
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a quasi-static situation
Explanation
The original form of Maxwell's circuital law relates magnetic fields to electric currents that produce them. It determines the magnetic field associated with a given current (static), or the current associated with a given magnetic field.
$$\bigtriangledown\times B=\mu_0 J$$
The circuital equation is extended by including the polarization current, thereby remedying the limited applicability of the original circuital law by Ampere. Thus it is for the non-static situation.
$$\bigtriangledown\times H=J_f+\dfrac{dD}{dt}$$
Fill in the blanks.
Current flowing through the resistor is known as ________
, while the current flowing through the capacitor is commonly known as _______.
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eddy current, displacement current
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displacement current , conduction current
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conduction current, eddy current
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conduction current, displacement current
Explanation
Current does not flow through the capacitor . But the current that flows out of one electrode of capacitor equals the current that flows in to the other electrode. The net effect is as if there is a current flowing through the path containing the capacitor. This is known as displacement current.
But current ac
tually flows through the resistor known as conduction current.
State whether true or false :
Ultraviolet rays are used to take photographs in darkness.
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True
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False
Explanation
Wrong
Infrared is used in dark for photography. All body emit infrared radiation every time.
Since infrared radiation is invisible, photography in total darkness can be readily carried out if infrared film is used and the light source is covered with a light-absorbing but infrared-transmitting filter.
Which of the following is/are electromagnetic wave(s)?
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Microwaves
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Radio wave
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Infrared radiation
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All of the above
Explanation
All the given waves are found in electromagnetic spectrum and have the properties of an electromagnetic wave, therefore all (microwave, radio waves, infrared radiation) are electromagnetic waves.
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