Class 12 Electromagnetic Waves CBSE Questions & Answers

Class 12 · Electromagnetic Waves

This is Physics Class 12 Electromagnetic Waves CBSE Questions & Answers. There are 15 questions in this test with each question having around four answer choices.

Questions & Answers

1
Calculate the frequency of red light with a wavelength of \({\rm{4}}.{\rm{2 }} \times {\rm{ 1}}{0^{ - {\rm{7}}}}\) m
  • A
    7.14 \( \times {\rm{ 1}}{0^{{\rm{14}}}}{\rm{Hz}}\)
    Correct
  • B
    7.34 \( \times {\rm{ 1}}{0^{{\rm{14}}}}{\rm{Hz}}\)
  • C
    7.64 \( \times {\rm{ 1}}{0^{{\rm{14}}}}{\rm{Hz}}\)
  • D
    7.94 \( \times {\rm{ 1}}{0^{{\rm{14}}}}{\rm{Hz}}\)
2
Ultraviolet radiation has a wavelength of 200 nm. What is the frequency of the radiation?
  • A
    1.6 \( \times {\rm{ 1}}{0^{{\rm{15}}}}\)
  • B
    1.5 \( \times {\rm{ 1}}{0^{{\rm{15}}}}\) Hz
    Correct
  • C
    1.8 \( \times {\rm{ 1}}{0^{{\rm{15}}}}\)
  • D
    1.7 \( \times {\rm{ 1}}{0^{{\rm{15}}}}\)
3
What is the energy of an ultraviolet photon with a wavelength of 200 nm?
  • A
    9.339 \( \times {\rm{ 1}}{0^{ - {\rm{1}}0}}\) J
  • B
    9.539 \( \times {\rm{ 1}}{0^{ - {\rm{1}}0}}\) J
  • C
    9.939 \( \times {\rm{ 1}}{0^{ - {\rm{1}}0}}\) J
    Correct
  • D
    9.739 \( \times {\rm{ 1}}{0^{ - {\rm{1}}0}}\) J
4
Electromagnetic waves propagate
  • A
    faster in a dielectric
  • B
    None of the above
  • C
    slower in a dielectric
    Correct
  • D
    at the same speed in a dielectric
5
Electromagnetic waves
  • A
    cannot form standing waves as they change phase while propagating
  • B
    can form standing waves on getting reflected
    Correct
  • C
    None of the above
  • D
    cannot form standing waves as they can only move in one direction
6
The intensity of a plane electromagnetic wave is proportional to
  • A
    Electric field cubed
  • B
    1/ Electric field squared
  • C
    Electric field squared
    Correct
  • D
    Electric field
7
A carbon dioxide laser emits a sinusoidal electromagnetic wave that travels in vacuum in the negative x-direction. The wavelength is 10.6µm and the field is parallel to the z-axis, with \({{\rm{E}}_{{\rm{max}}}}\) = 1.5MV/m Vector equation for E as functions of time and position is
  • A
    E(x, t) = \({{\rm{E}}_{{\rm{max}}}}\left( {{\rm{5}}.{\rm{93 }} \times {\rm{ 1}}{0^{\rm{5}}}{\rm{rad}}/{\rm{m x }} + {\rm{ 1}}.{\rm{78 }} \times {\rm{1}}{0^{{\rm{14}}}}{\rm{rad}}/{\rm{s t}}} \right)\)
  • B
    E(x, t) = \( - {\rm{ }}{{\rm{E}}_{{\rm{max}}}}\left( {{\rm{5}}.{\rm{93 }} \times {\rm{ 1}}{0^{\rm{5}}}{\rm{rad}}/{\rm{m x }} + {\rm{ 1}}.{\rm{78 }} \times {\rm{1}}{0^{{\rm{14}}}}{\rm{rad}}/{\rm{s t}}} \right)\)
  • C
    E(x, t) = \({{\rm{E}}_{{\rm{max}}}}{\rm{cos}}\left( {{\rm{5}}.{\rm{93 }} \times {\rm{ 1}}{0^{\rm{5}}}{\rm{rad}}/{\rm{m x }} + {\rm{ 1}}.{\rm{78 }} \times {\rm{1}}{0^{{\rm{14}}}}{\rm{rad}}/{\rm{s t}}} \right)\)
    Correct
  • D
    E(x, t) = \({{\rm{E}}_{{\rm{max}}}}{\rm{cos}}\left( {{\rm{5}}.{\rm{93 }} \times {\rm{ 1}}{0^{\rm{5}}}{\rm{rad}}/{\rm{m x }} - {\rm{ 1}}.{\rm{78 }} \times {\rm{1}}{0^{{\rm{14}}}}{\rm{rad}}/{\rm{s t}}} \right)\)
8
How much time does it take light to travel from the moon to the earth, a distance of 384,000 km?
  • A
    1.58 s
  • B
    1.48 s
  • C
    1.38 s
  • D
    1.28 s
    Correct
9
Light from the star Sirius takes 8.61 years to reach the earth. What is the distance from earth to Sirius in kilometers?
  • A
    7.85 \( \times {\rm{ 1}}{0^{{\rm{13}}}}\) km
  • B
    8.05 \( \times {\rm{ 1}}{0^{{\rm{13}}}}\) km
  • C
    7.95 \( \times {\rm{ 1}}{0^{{\rm{13}}}}\) km
  • D
    8.15 \( \times {\rm{ 1}}{0^{{\rm{13}}}}\) km
    Correct
10
A sinusoidal electromagnetic wave is propagating in vacuum in the +z-direction. If at a particular instant and at a certain point in space the electric field is in the and has magnitude 4.00 V/m what are the magnitude and direction of the magnetic field of the wave at this same point in space and instant in time?
  • A
    12.7 nT, +y-direction
  • B
    13.0 nT, -y-direction
  • C
    12.4 nT, +y-direction
  • D
    13.3 nT, +y-direction
    Correct
11
Medical x rays are taken with electromagnetic waves having a wavelength of around 0.10 nm. What are the frequency and period of such waves?
  • A
    \({\rm{3}}.{\rm{2 }} \times {\rm{ 1}}{0^{{\rm{15}}}}{\rm{Hz}},{\rm{ 3}}.{\rm{3 }} \times {\rm{ 1}}{0^{ - {\rm{17}}}}{\rm{s}}\)
  • B
    \({\rm{3}}.{\rm{2 }} \times {\rm{ 1}}{0^{{\rm{15}}}}{\rm{Hz}},{\rm{ 3}}.{\rm{3 }} \times {\rm{ 1}}{0^{ - {\rm{17}}}}{\rm{s}}\)
  • C
    \({\rm{3}}.{\rm{4 }} \times {\rm{ 1}}{0^{{\rm{15}}}}{\rm{Hz}},{\rm{ 3}}.{\rm{3 }} \times {\rm{ 1}}{0^{ - {\rm{17}}}}{\rm{s}}\)
  • D
    \({\rm{3 }} \times {\rm{ 1}}{0^{{\rm{15}}}}{\rm{Hz}},{\rm{ 3}}.{\rm{3 }} \times {\rm{ 1}}{0^{ - {\rm{17}}}}{\rm{s}}\)
    Correct
12
Radio station WCCO in Minneapolis broadcasts at a frequency of 830 kHz. Wavelength and wave number are
  • A
    391 m, 0.0174 rad/m
  • B
    371 m, 0.0174 rad/m
  • C
    381 m, 0.0174 rad/m
  • D
    361 m, 0.0174 rad/m
    Correct
13
An electromagnetic wave with frequency 5.70 \( \times {\rm{ 1}}{0^{{\rm{14}}}}\) propagates with a speed of 2.17\( \times {\rm{ 1}}{0^{\rm{8}}}\) in a certain piece of glass. Find (a) the wavelength of the wave in the glass; (b) the wavelength of a wave of the same frequency propagating in air.
  • A
    a) 0.411 \(\mu {\rm{m}}\) b) 0.556 \(\mu {\rm{m}}\)
  • B
    a) 0.381 \(\mu {\rm{m}}\) b) 0.526 \(\mu {\rm{m}}\)
    Correct
  • C
    a) 0.401 \(\mu {\rm{m}}\) b) 0.546 \(\mu {\rm{m}}\)
  • D
    a) 0.391 \(\mu {\rm{m}}\) b) 0.536 \(\mu {\rm{m}}\)
14
According to Maxwell’s equations
  • A
    Electric and magnetic fields are coupled
    Correct
  • B
    Electric and magnetic fields are independent of each other
  • C
    Electric and magnetic fields are decoupled
  • D
    Electric and magnetic fields move around in circles
15
Velocity of plane electromagnetic waves in vacuum equals
  • A
    \({2 \over {\sqrt {{\mu _0}{_0}} }}\)
  • B
    \({1 \over {\sqrt {{\mu _0}{_0}} }}\)
    Correct
  • C
    \({\mu _0}{\varepsilon _0}\)
  • D
    \(\sqrt {{\mu _0}{\varepsilon _0}} \)