# MCQs for Physics Class 12 with Answers Chapter 8 Electromagnetic Waves

Students of class 12 Physics should refer to MCQ Questions Class 12 Physics Electromagnetic Waves with answers provided here which is an important chapter in Class 12 Physics NCERT textbook. These MCQ for Class 12 Physics with Answers have been prepared based on the latest CBSE and NCERT syllabus and examination guidelines for Class 12 Physics. The following MCQs can help you to practice and get better marks in the upcoming class 12 Physics examination

## Chapter 8 Electromagnetic Waves MCQ with Answers Class 12 Physics

MCQ Questions Class 12 Physics Electromagnetic Waves provided below have been prepared by expert teachers of grade 12. These objective questions with solutions are expected to come in the upcoming Standard 12 examinations. Learn the below provided MCQ questions to get better marks in examinations.

Question. One requires 11 eV of energy to dissociate a carbon monoxide molecule into carbon andoxygen atoms. The minimum frequency of the appropriate electromagnetic radiation to achieve the dissociation lies in
(a) visible region
(b) infrared region
(c) ultraviolet region
(d) microwave region

C

Question. A linearly polarised electromagnetic wave given as E E0 i cos (kz – ϖt) = t ~ is incident normally on a perfectly reflecting infinite wall at z = a. Assuming that the material of the wall is optically inactive, the reflected wave will be given as

B

Question. If E and B represent electric and magnetic field vectors of the electromagnetic wave, the direction of propagation of electromagnetic wave is along .
(a) E
(b) B
(c) B × E
(d) E × B

D

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

B

Question. If we want to produce electromagnetic waves of wavelength 500 km by an oscillating charge; then frequency of oscillating charge must be
(a) 600 Hz
(b) 500 Hz
(c) 167 Hz
(d) 15 Hz

A

Question. The rms value of the electric field of light coming from the sun is 720 N/C. The average total energy density of the electromagnetic wave is :
(a) 4.58 × 10–6 J/m3
(b) 6.37 × 10–9 J/m3
(c) 1.35 × 10–12 J/m3
(d) 3.3 × 10–3 J/m3

A

Question. A plane electromagnetic wave travelling along X-axis has a wavelength 10.0 mm. The electric field points along Y-direction and has peak value of 30 V/m. Then the magnetic field in terms of x in metre and t in second may be expressed as

B

Question. A plane electromagnetic wave propagating along x direction can have the following pairs of E and B
(a) Ex, By
(b) Ey, Bz
(c) Bx, Ey
(d) Ez, By

B, D

Question. Electromagnetic waves travelling in a medium having relative permeability 1.3 ∈r = and relative permittivity 2.14 μr = . The speed of electromagnetic waves in medium must be
(a) 1.8 × 108 m/s
(b) 1.8 × 104 m/s
(c) 1.8 × 106 m/s
(d) 1.8 × 102 m/s

A

Question. Light with an energy flux of 20 W/cm2 falls on a non-reflecting surface at normal incidence. If the surface has an area of 30 cm2, the total momentum delivered (for complete absorption) during 30 minutes is.
(a) 36 × 10–5 kg m/s
(b) 36 × 10–4 kg m/s
(c) 108 × 104 kg m/s
(d) 1.08 × 107 kg m/s

B

Question. Electromagnetic waves travelling in a medium has speed 2 × 108 m/s. If the relative permeability is 1, then the relative permittivity of medium must be
(a) 2
(b) 2.25
(c) 2.5
(d) 1.5

B

Question. The radiowaves of wavelength 360 m are transmitted from a transmitter. The inductance of the coil which must be connected with capacitor of capacitance 3.6 μF in a resonant circuit to receive these waves will be nearly
(a) 103 H
(b) 102 H
(c) 10–4 H
(d) 10–8 H

D

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

C

Question. A 100 Ω resistance and a capacitor of 100 Ω reactance are connected in series across a 22 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. An electromagnetic wave radiates outwards from a dipole antenna, with E0 as the amplitude of its electric field vector. The electric field E0 which transports significant energy from the source falls off as
(a) 1/r3
(b) 1/r2
(c) 1/r
(d) remains constant

C

Question. An LC circuit contains inductance L = 1mH and capacitance C = 0.01 μF. The wavelength of the electromagnetic wave generated is nearly
(a) 0.5 m
(b) 5 m
(c) 30 m
(d) 188 m

D

Question. The electric field intensity produced by the radiations coming from 100 W bulb at a 3 m distance is E. The electric field intensity produced by the radiations coming from 50 W bulb at the same distance is.
(a) E/2
(b) 2E
(c) E/√2
(d) √2E

C

Question. A plane electromagnetic wave of energy U is reflected from the surface. Then the momentum transferred by electromagnetic wave to the surface is
(a) 0
(b) U/c
(c) 2U/c
(d) U/2c

C

Question. What is the amplitude of electric field produced by radiation coming from a 100 W bulb at a distance of 4 m? The efficiency of bulb is 3.14% and it may be assumed as a point source.
(a) 2.42 V/m
(b) 3.43 V/m
(c) 4.2 × 104 V/m
(d) 14 × 104 V/m

B

Question. The electromagnetic radiation used in food processing sterilizing agent is
(a) microwaves
(b) UV rays
(c) gamma rays

B

Question. An electromagnetic wave is made up of joint electric (E) and magnetic (B) fields. Its direction of propagation is
(a) parallel to E
(b) perpendicular to E but parallel to B
(c) parallel to B
(d) perpendicular to both E and B

A

Question. The frequency modulated waves are
(a) reflected by atmosphere
(b) absorbed by atmosphere
(c) bend by atmosphere

C

Question. If λ =1´104 Å then it corresponds to
(a) infrared
(b) microwaves
(c) ultraviolet
(d) X-rays

A

Question. 10 cm is a wavelength corresponding to the spectrum of
(a) infrared rays
(b) ultra-violet rays
(c) microwaves
(d) ϒ -rays

C

Question. A plane electromagnetic wave travels in free space along x-axis. At a particular point in space, the electric field along y-axis is 9.3V m–1. The magnetic induction (B) along z-axis is
(a) 3.1 × 10–8 T
(b) 3 × 10–5 T
(c) 3 × 10–6 T
(d) 9.3 × 10–6 T

A

Question. Which of the following statement is false for the properties of electromagnetic waves?
(a) Both electric and magnetic field vectors attain the maxima 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. 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. The frequencies of X-rays, g-rays and ultraviolet rays are respectively a, b and c then
(a) a < b, b > c
(b) a > b, b > c
(c) a > b, b < c
(d) a < b, b < c

A

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, micro-waves
(c) microwaves, gamma rays, infrared, ultraviolet
(d) infrared, microwave, ultraviolet, gamma rays

A

Question. Which of the following radiations has the least wavelength ?
(a) γ -rays
(b) β -rays
(c) α -rays
(d) X -rays

A

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

D

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

C

Question. Pick out the longest wavelength from the following types of radiation.
(a) blue light
(b) gamma rays
(c) X-rays
(d) red light

D

Question. One requires 11 eV of energy to dissociate a carbon monoxide molecule into carbon and oxygen atoms. The minimum frequency of the appropriate electromagnetic radiation to achieve the dissociation lies in
(a) visible region
(b) infrared region
(c) ultraviolet region
(d) microwave region

C

Question. The frequency of electromagnetic wave, which is 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. The electric and the magnetic field associated with an E.M. wave, propagating along the +z-axis, can be represented by

A

Question. A linearly polarised electromagnetic wave given as E = E0 ˆi cos (kz -ϖt) is incident normally on a perfectly reflecting infinite wall at z = a. Assuming that the material of the wall is optically inactive, the reflected wave will be given as
(a) Er = E0 ˆi (kz -ϖt)
(b) Er = E0 ˆi cos (kz + ϖt)
(c) Er = E0 ˆi cos (kz + ϖt)
(d) Er = E0 ˆi sin (kz -ϖt)

B

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

C

Question. The electric field intensity produced by the radiations coming from 100 W bulb at a 3 m distance is E. The electric field intensity produced by the radiations coming from 50 W bulb at the same distance is
(a) E/2
(b) 2E
(c) 2/√2
(d) √2E

C

Question. Light with an energy flux of 20 W/cm2 falls on a non-reflecting surface at normal incidence. If the surface has an area of 30 cm2, the total momentum delivered (for complete absorption) during 30 min is
(a) 36 × 10–5 kg-m/s
(b) 36 × 10–4 kg-m/s
(c) 108 × 104 kg-m/s
(d) 1.08 × 107 kg-m/s

B

Question. If E and B represent electric and magnetic field vectors of the electromagnetic wave, the direction of propagation of electromagnetic wave is along
(a) E
(b) B
(c) B × E
(d) E × B

D

Question. An EM wave radiates outwards from a dipole antenna, with E0 as the amplitude of its electric field vector. The electric field E0 which transports significant energy from the source falls off as
(a) 1/r2
(b) 1/r2
(c) 1/r
(d) remains constant

C

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

C

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

D

Question. Light with an energy flux of 25 × 104 Wm– 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. Out of the following options which one can be used to produce a propagating electromagnetic wave ?
(a) A charge moving at constant velocity
(b) A stationary charge
(c) A chargeless particle
(d) An accelerating charge

D

Question. A radiation of energy ‘E’ falls normally on a perfectly reflecting surface. The momentum transferred to the surface is (C = Velocity of light)
(a) 2E/C
(b) 2E/C2
(c) E/C2
(d) E/C

A

Question. In an electromagnetic wave in free space the root mean square value of the electric field is Erms = 6V/m. 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. An electromagnetic wave travels in vacuum along z-direction E = (E1 iˆ + E2 ˆj) cos (kz -ϖt) Choose the correct options from the following
(a) The associated magnetic field is given as B = 1/c (E1 iˆ + E2 ˆj) cos (kz -ϖt
(b) The associated magnetic field is given as B = 1/c (E1 iˆ + E2 ˆj) cos (kz -ϖt
(c) The given electromagnetic field is circularly polarised
(d) The given electromagnetic wave is plane polarised

D

#### Fill in the Blanks

Question. _________________ particles radiate electromagnetic waves.

Accelerated charged

Question. The displacement current is precisely equal to the conduction current, when the two are present in different parts of the circuit. These currents are individually discontinuous, but the two currents together posses the property of _________________ through any closed circuit.

continuity

Question. The _________________ of electromagnetic waves does not change when it goes from one medium to another but its wavelength changes.

frequency

Question. The orderly distribution of electromagnetic radiations according to their frequency or wavelength is called _________________.

electromagnetic spectrum

Question. The shortest wavelength radio waves are called _________________.

micro-waves

Question. Electromagnetic waves are not _________________ by electric and magnetic waves.

deflected

Question. The current which comes into play in the region, whenever the electric field and hence the electric flux is changing with time is called _________________.

displacement current

Question. Ozone layer in the atmosphere plays a protective role, and hence its depletion by _____________ gas is a matter of international concern

chlorofluorocarbons (CFCs)

Question. Electromagnetic wave is _________________ in nature as the electric and magnetic fields are perpendicular to each other and to the direction of propagation of the wave.