# MCQs For NCERT Class 12 Physics Chapter 8 Electromagnetic Waves

Please refer to the MCQ Questions for Class 12 Physics Chapter 8 Electromagnetic Waves with Answers. The following Electromagnetic Waves Class 12 Physics MCQ Questions have been designed based on the latest syllabus and examination pattern for Class 12. Our experts have designed MCQ Questions for Class 12 Physics with Answers for all chapters in your NCERT Class 12 Physics book.

## Electromagnetic Waves Class 12 MCQ Questions with Answers

See below Electromagnetic Waves Class 12 Physics MCQ Questions, solve the questions and compare your answers with the solutions provided below.

Question. A parallel plate capacitor of capacitance 20 mF is being charged by a voltage source whose potential is changing at the rate of 3 V/s. The conduction current through the connecting wires, and the displacement current through the plates of the capacitor, would be, respectively
(a) zero, zero
(b) zero, 60 mA
(c) 60 mA, 60 mA
(d) 60 mA, zero

C

Question. The frequency order for g-rays (B), X-rays (A),UV rays (C) is
(a) B > A > C
(b) A > B > C
(c) C > B > A
(d) A > C > B.

A

Question. A 100 W resistance and a capacitor of 100 W reactance are connected in series across a 220 V source. When the capacitor is 50% charged, the peak value of the displacement current is
(a) 2.2 A
(b) 11 A
(c) 4.4 A
(d) 11 2 A

A

Question. Light with an average flux of 20 W/cm2 falls on a non-reflecting surface at normal incidence having surface area 20 cm2. The energy received by the surface during time span of 1 minute is
(a) 10 × 103 J
(b) 12 × 103 J
(c) 24 × 103 J
(d) 48 × 103 J

C

Question. Wavelength of light of frequency 100 Hz is
(a) 4 × 106 m
(b) 3 × 106 m
(c) 2 × 106 m
(d) 5 × 10–5 m

B

Question. The energy of the em waves is of the order of 15 keV.
To which part of the spectrum does it belong?
(a) Ultraviolet rays
(b) g-rays
(c) X-rays
(d) Infra-red rays

C

Question. The ratio of contributions made by the electric field and magnetic field components to the intensity of an electromagnetic wave is (c = speed of electromagnetic waves)
(a) c : 1
(b) 1 : 1
(c) 1 : c
(d) 1 : c2

B

Question. A new system of unit is evolved in which the values of μ0 and ∈0 are 2 and 8 respectively. Then the speed of light in this system will be
(a) 0.25
(b) 0.5
(c) 0.75
(d) 1

A

Question. An electromagnetic wave of frequency n = 3.0 MHz passes from vacuum into a dielectric medium with permittivity ∈= 4.0 . Then
(a) wavelength is halved and frequency remains unchanged
(b) wavelength is doubled and frequency becomes half
(c) wavelength is doubled and the frequency remains unchanged
(d) wavelength and frequency both remain unchanged

A

Question. In an electromagnetic wave
(a) power is transmitted along the magnetic field
(b) power is transmitted along the electric field
(c) power is equally transferred along the electric and magnetic fields
(d) power is transmitted in a direction perpendicular to both the fields

D

Question. Ozone layer blocks the radiations of wavelength
(a) more than 3 × 10–7 m
(b) equal to 3 × 10–7 m
(c) less than 3 × 10–7 m
(d) all of these

D

Question. An em wave is propagating in a medium with a velocity v = v ^i . The instantaneous oscillating electric field of this em wave is along +y axis. Then the direction of oscillating magnetic field of the em wave will be along
(a) –z direction
(b) +z direction
(c) –y direction
(d) –x direction

B

Question. The frequency of electromagnetic wave, which best suited to observe a particle of radius 3 × 10–4 cm is of the order of
(a) 1015
(b) 1014
(c) 1013
(d) 1012

B

Question. In an electromagnetic wave in free space the root mean square value of the electric field is Erms = 6 V m–1. The peak value of the magnetic field is
(a) 2.83 × 10–8 T
(b) 0.70 × 10–8 T
(c) 4.23 × 10–8 T
(d) 1.41 × 10–8 T

A

Question. Out of the following options which one can be used to produce a propagating electromagnetic wave ?
(a) A chargeless particle
(b) An accelerating charge
(c) A charge moving at constant velocity
(d) A stationary charge

B

Question. The structure of solids is investigated by using
(a) cosmic rays
(b) X-rays
(c) g-rays

B

Question. A wave is propagating in a medium of electric dielectric constant 2 and relative magnetic permeability 50. The wave impedance of such a medium is
(a) 5 Ω
(b) 376.6 Ω
(c) 1883 Ω
(d) 3776 Ω

C

Question. The frequency of electromagnetic wave, which best suited to observe a particle of radii 3 × 10–4 cm is of the order of
(a) 1015
(b) 1014
(c) 1013
(d) 1012

A

Question. Light with an energy flux of 25 × 104 W m–2 falls on a perfectly reflecting surface at normal incidence. If the surface area is 15 cm2, the average force exerted on the surface is
(a) 1.25 × 10–6 N
(b) 2.50 × 10–6 N
(c) 1.20 × 10–6 N
(d) 3.0 × 10–6 N

B

Question. An electromagnetic wave of frequency u = 3.0 MHz passes from vacuum into a dielectric medium with relative permittivity e = 4.0. Then
(a) Wavelength is doubled and frequency becomes half.
(b) Wavelength is halved and frequency remains unchanged.
(c) Wavelength and frequency both remain unchanged.
(d) Wavelength is doubled and frequency unchanged

B

Question. An electromagnetic wave is propagating along Y-axis. Then
(a) oscillating electric field is along X-axis and oscillating magnetic field is along Y-axis
(b) oscillating electric field is along Z-axis and oscillating magnetic field is along X-axis
(c) both oscillating electric and magnetic fields are along Y-axis, but phase difference between them is 90°
(d) both oscillating electric and magnetic fields are mutually perpendicular in arbitrary direction

B

Question. The frequency of electromagnetic wave, which best suited to observe a particle of radii 3 × 10–4 cm is of the order of
(a) 1015
(b) 1014
(c) 1013
(d) 1012

A

Question. The electric field associated with an em wave in vacuum is given by [E = i ^ 40 cos (kz – 6 × 108t)]; where E, z and t are in volt/m, meter and seconds respectively. The value of wave vector k is
(a) 2 m–1
(b) 0.5 m–1
(c) 6 m–1
(d) 3 m–1

A

Question. A plane electromagnetic wave is incident on a material surface. If the wave delivers momentum p and energy E, then
(a) p = 0, E = 0
(b) p ≠ 0, E ≠ 0
(c) p ≠ 0, E = 0
(d) p = 0, E ≠ 0

B

Question. All components of the electromagnetic spectrum in vacuum have the same
(a) energy
(b) velocity
(c) wavelength
(d) frequency

B

Question. Approximate height of ozone layer above the ground is
(a) 60 to 70 km
(b) 59 km to 80 km
(c) 70 km to 100 km
(d) 100 km to 200 km

A

Question. In which one of the following regions of the electromagnetic spectrum will the vibrational motion of molecules give rise to absorption ?
(a) Ultraviolet
(b) Microwaves
(c) Infrared

B

Question. The ratio of amplitude of magnetic field to the amplitude of electric field for an electromagnetic wave propagating in vacuum is equal to
(a) the speed of light in vacuum
(b) reciprocal of speed of light in vacuum
(c) the ratio of magnetic permeability to the electric susceptibility of vacuum
(d) unity.

B

Question. In an electromagnetic wave, the electric and magnetic fields are 100 V m–1 and 0.265 A m–1. The maximum energy flow is
(a) 26.5 W/m2
(b) 36.5 W/m2
(c) 46.7 W/m2
(d) 765 W/m2

A

Question. If lv, lx and lm represent the wavelengths of visible light, X-rays and microwaves respectively, then
(a) lm > lx > lv
(b) lm > lv > lx
(c) lv > lx > lm
(d) lv > lm > lx.

B

Question. Which of the following rays are not electromagnetic waves ?
(a) X-rays
(b) g-rays
(c) b-rays
(d) heat rays

C

Question. Which of the following statement is false for the properties of electromagnetic waves ?
(a) Both electric and magnetic field vectors attain the maxim and minima at the same place and same time.
(b) The energy in electromagnetic wave is divided equally between electric and magnetic vectors.
(c) Both electric and magnetic field vectors are parallel to each other and perpendicular to the direction of propagation of wave.
(d) These waves do not require any material medium for propagation

C

Question. Biological importance of ozone layer is
(a) it stops ultraviolet rays
(b) ozone layer reduces green house effect
(c) ozone layer reflects radio waves
(d) ozone layer controls O2/H2 ratio in atmosphere.

A

Question. For a transparent medium relative permeability and permittivity, μr and er are 1.0 and 1.44 respectively. The velocity of light in this medium would be
(a) 2.5 × 108 m/s
(b) 3 × 108 m/s
(c) 2.08 × 108 m/s
(d) 4.32 × 108 m/s

A

Question. The electric field of an electromagnetic wave in free space is given by →E = 10cos(107 t + kx)jˆ V /m , where t and x are in seconds and metres respectively. It can be inferred that
(1) the wavelength l is 188.4 m.
(2) the wave number k is 0.33 rad/m.
(3) the wave amplitude is 10 V/m.
(4) the wave is propagating along +x direction.
Which one of the following pairs of statements is correct?
(a) (3) and (4)
(b) (1) and (2)
(c) (2) and (3)
(d) (1) and (3)

D

Question. A signal emitted by an antenna from a certain point can be received at another point of the surface in the form of   D
(a) sky wave
(b) ground wave
(c) sea wave
(d) both (a) and (b)

D

Question. We consider the radiation emitted by the human body. Which one of the following statements is true?
(a) The radiation emitted is in the infrared region.
(b) The radiation is emitted only during the day.
(c) The radiation is emitted during the summers and absorbed during the winters.
(d) The radiation emitted lies in the ultraviolet region and hence is not visible.

A

Question. Which of the following electromagnetic radiations have the longest wavelength ?
(a) X-rays
(b) g-rays
(c) Microwaves

D

Question. The electric and magnetic field of an electromagnetic wave are
(a) in opposite phase and perpendicular to each other
(b) in opposite phase and parallel to each other
(c) in phase and perpendicular to each other
(d) in phase and parallel to each other.

C

Question. The velocity of electromagnetic wave is parallel to
(a) B × E
(b) E × B
(c) E
(d) B

B

Question. The condition under which a microwave oven heats up a food item containing water molecules most efficiently is
(a) microwaves are heat waves, so always produce heating
(b) infra-red waves produce heating in a microwave oven
(c) the frequency of the microwaves must match the resonant frequency of the water molecules
(d) the frequency of the microwaves has no relation with natural frequency of water molecules.

C

Question. The decreasing order of wavelength of infrared, microwave, ultraviolet and gamma rays is
(a) microwave, infrared, ultraviolet, gamma rays
(b) gamma rays, ultraviolet, infrared, microwaves
(c) microwaves, gamma rays, infrared, ultraviolet
(d) infrared, microwave, ultraviolet, gamma rays

A

Question. What is the cause of Green house effect?
(a) Infra-red rays
(b) Ultra violet rays
(c) X-rays

A

Question. Which of the following electromagnetic radiations have the smaller wavelength?
(a) X-rays
(b) g-rays
(c) UV waves
(d) microwaves

B

Question. Radio waves diffract around building although light waves do not. The reason is that radio waves
(a) travel with speed larger than c
(b) have much larger wavelength than light
(c) are not electromagnetic waves
(d) None of these

B

Question. Biological importance of ozone layer is
(a) it stops ultraviolet rays
(b) ozone layer reduce green house effect
(c) ozone layer reflects radio waves
(d) ozone layer controls O2 / H2 radio in atmosphere

A

Question. The energy of electromagnetic wave in vacuum is given by the relation

D

Question. If ∈0 and μ0 are the electric permittivity and magnetic permeability in vacuum, e and m are corresponding quantities in medium, then refractive index of the medium is

D

Question. The relation between electric field E and magnetic field H in an electromagnetic wave is