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
Electromagnetic waves for TV and radio have a frequency about
  • A
    750 KHz
    Correct
  • B
    750 MHz
  • C
    750 Hz
  • D
    750 GHz
2
Microwaves have a frequency of about
  • A
    10 KHz
  • B
    10 MHz
  • C
    10 GHz
    Correct
  • D
    10 Hz
3
Food is heated in a microwave oven because
  • A
    Radiation from oven walls heats the food
  • B
    Oven walls conductively heat the food
  • C
    Water molecules absorb microwave radiation
    Correct
  • D
    Resistance heating takes place supplying heat to the food
4
Infrared waves are produced by
  • A
    static charges
  • B
    dipole oscillations
  • C
    all hot bodies and molecules
    Correct
  • D
    Permanent magnets
5
Infrared waves are sometimes referred to as heat waves because
  • A
    water molecules present in most materials readily reradiate infrared waves
  • B
    water molecules present in most materials readily absorb infrared waves
    Correct
  • C
    water molecules present in most materials readily transmit infrared waves
  • D
    water molecules present in most materials readily reflect infrared waves
6
Visible range of electromagnetic spectrum is
  • A
    400 nm to 0.6 nm
    Correct
  • B
    400 m to 0.6 m
  • C
    400 µm to 0.6 µm
  • D
    400 mm to 0.6 mm
7
Tanning of the skin in sunlight is due to
  • A
    infrared
  • B
    cosmic rays
  • C
    visible light
  • D
    UV radiation
    Correct
8
Comparing X-rays and Gamma rays
  • A
    Gamma rays have more speed than X-rays
  • B
    Gamma rays have larger wavelength than X-rays
  • C
    Gamma rays have more energy than X-rays
    Correct
  • D
    Gamma rays are less penetrating than X-rays
9
A parallel plate capacitor with circular plates of radius 1 m has a capacitance of 1 \({\rm{nF}}\). At t = 0, it is connected for charging in series with a resistor R = 1 M\(\Omega \) across a 2V battery. Calculate the magnetic field at a point P, halfway between the centre and the periphery of the plates, after t = \({\rm{1}}{0^{ - {\rm{3}}}}\) s. (The charge on the capacitor at time t is q (t) = CV [1 – exp (–\({\rm{t}}/\tau \))], where the time constant τ is equal to CR.)
Question 9 figure 1
  • A
    0.68 \( \times {\rm{ 1}}{0^{-{\rm{13}}}}{\rm{T}}\) Hz
  • B
    0.64 \( \times {\rm{ 1}}{0^{-{\rm{13}}}}{\rm{T}}\)
  • C
    0.54 \( \times {\rm{ 1}}{0^{-{\rm{13}}}}{\rm{T}}\)
  • D
    0.74 \( \times {\rm{ 1}}{0^{-{\rm{13}}}}{\rm{T}}\)
    Correct
10
Plane electromagnetic wave of frequency 25 MHz travels in free space along the x-direction. At a particular point in space and time, E = 6.3 j V/m. B at this point is
  • A
    B = 1.8 \( \times {\rm{ 1}}{0^{-{\rm{8}}}}{\bf{k}}{\rm{T}}\)
  • B
    B = 1.6 \( \times {\rm{ 1}}{0^{-{\rm{8}}}}{\bf{k}}{\rm{T}}\)
  • C
    B = 2.1 \( \times {\rm{ 1}}{0^{-{\rm{8}}}}{\bf{k}}{\rm{T}}\)
    Correct
  • D
    B = 1.5 \( \times {\rm{ 1}}{0^{-{\rm{8}}}}{\bf{k}}{\rm{T}}\)
11
The magnetic field in a plane electromagnetic wave is given by By =\({\rm{2 }} \times {\rm{ 1}}{0^{-{\rm{7}}}}{\rm{sin }}\left( {0.{\rm{5}} \times {\rm{1}}{0^{\rm{3}}}{\rm{x}} + {\rm{1}}.{\rm{5}} \times {\rm{1}}{0^{{\rm{11}}}}{\rm{t}}} \right){\rm{ T}}\). Wavelength and frequency of the wave are
  • A
    1.20 cm, 22.9 GHz
  • B
    1.06 cm, 21.9 GHz
  • C
    1.16 cm, 23.9 GHz
  • D
    1.26 cm, 23.9 GHz
    Correct
12
Light with an energy flux of 18 W/ \({\rm{c}}{{\rm{m}}^{\rm{2}}}\) falls on a nonreflecting surface at normal incidence. If the surface has an area of 20 \({\rm{c}}{{\rm{m}}^{\rm{2}}}\), Average force exerted on the surface during a 30 minute time span is
  • A
    1.4 \( \times {\rm{ 1}}{0^{ - {\rm{6}}}}{\rm{N}}\)
  • B
    1.2 \( \times {\rm{ 1}}{0^{ - {\rm{6}}}}{\rm{N}}\)
    Correct
  • C
    1.3 \( \times {\rm{ 1}}{0^{ - {\rm{6}}}}{\rm{N}}\)
  • D
    1.5 \( \times {\rm{ 1}}{0^{ - {\rm{6}}}}{\rm{N}}\)
13
Calculate the electric and magnetic fields produced by the radiation coming from a 100 W bulb at a distance of 3 m. Assume that the efficiency of the bulb is 2.5% and it is a point source
  • A
    4.01 V/m, \({\rm{9}}.{\rm{6 }} \times {\rm{ 1}}{0^{ - {\rm{9}}}}{\rm{T}}\)
  • B
    3.77 V/m, \({\rm{9}}.{\rm{6 }} \times {\rm{ 1}}{0^{ - {\rm{9}}}}{\rm{T}}\)
  • C
    3.87 V/m, \({\rm{9}}.{\rm{6 }} \times {\rm{ 1}}{0^{ - {\rm{9}}}}{\rm{T}}\)
  • D
    4.07 V/m, \({\rm{9}}.{\rm{6 }} \times {\rm{ 1}}{0^{ - {\rm{9}}}}{\rm{T}}\) `
    Correct
14
Figure shows a capacitor made of two circular plates each of radius 12 cm, and separated by 5.0 cm. The capacitor is being charged by an external source (not shown in the figure). The charging current is constant and equal to 0.15A. Capacitance and the rate of charge of potential difference between the plates are
Question 14 figure 1
  • A
    67.1 \({\rm{pF}},{\rm{ 1}}.{\rm{87 }} \times {\rm{ 1}}{0^{\rm{9}}}{\rm{V }}{{\rm{s}}^{-{\rm{1}}}}\)
  • B
    80.1 \({\rm{pF}},{\rm{ 1}}.{\rm{87 }} \times {\rm{ 1}}{0^{\rm{9}}}{\rm{V }}{{\rm{s}}^{-{\rm{1}}}}\)
    Correct
  • C
    74.1 \({\rm{pF}},{\rm{ 1}}.{\rm{87 }} \times {\rm{ 1}}{0^{\rm{9}}}{\rm{V }}{{\rm{s}}^{-{\rm{1}}}}\)
  • D
    70.1 \({\rm{pF}},{\rm{ 1}}.{\rm{87 }} \times {\rm{ 1}}{0^{\rm{9}}}{\rm{V }}{{\rm{s}}^{-{\rm{1}}}}\)
15
Figure shows a capacitor made of two circular plates each of radius 12 cm, and separated by 5.0 cm. The capacitor is being charged by an external source (not shown in the figure). The charging current is constant and equal to 0.15A. Displacement current across the plates is
Question 15 figure 1
  • A
    0.17 A.
  • B
    0.16 A.
  • C
    0.18 A.
  • D
    0.15 A.
    Correct