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NCERT Exemplar · Class 12 · Physics

Chapter 8: Electromagnetic Waves

Practice each question, then open the answer or worked solution.

Questions

32 questions
Q8.1Written answer

One requires 11eV 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

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Worked solution

c) ultraviolet region

Q8.2Written answer

A linearly polarized electromagnetic wave given as
Exemplar Solutions Class 12 Physics Chapter 8 - 1 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)

Exemplar Solutions Class 12 Physics Chapter 8 - 2

b)

Exemplar Solutions Class 12 Physics Chapter 8 - 3

c)

Exemplar Solutions Class 12 Physics Chapter 8 - 4

d)

Exemplar Solutions Class 12 Physics Chapter 8 - 5

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Worked solution

b)

Exemplar Solutions Class 12 Physics Chapter 8 - 6

Q8.3Written answer

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 30cm2, the total momentum delivered 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

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Worked solution

b) 36 × 10-4 kg m/s

Q8.4Written answer

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

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Worked solution

c) E/√2

Q8.5Written answer

If E and B represent electric and magnetic field vectors of the electromagnetic wave, the direction of propagation of the electromagnetic wave is along

a) E

b) B

c) B × E

d) E × B

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Worked solution

d) E × B

Q8.6Written answer

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

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Worked solution

c) 1: 1

Q8.7Multiple choice

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

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Correct option: C
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Worked solution

c) 1/r

Multiple Choice Questions II
Q8.8Multiple choice

An electromagnetic wave travels in vacuum along z-direction:
Exemplar Solutions Class 12 Physics Chapter 8 - 7. Choose the correct options from the following:

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Correct option: A
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Worked solution

a) the associated magnetic field is given as
Exemplar Solutions Class 12 Physics Chapter 8 - 10

d) the given electromagnetic waves is plane polarised

Q8.9Written answer

An electromagnetic wave travelling along the z-axis is given as: E = E0 cos (kz – ꞷt). Choose the correct options from the following

a) the associated magnetic field is given as
Exemplar Solutions Class 12 Physics Chapter 8 - 11

b) the electromagnetic field can be written in terms of the associated magnetic field as
Exemplar Solutions Class 12 Physics Chapter 8 - 12

c)
Exemplar Solutions Class 12 Physics Chapter 8 - 13

d)
Exemplar Solutions Class 12 Physics Chapter 8 - 14

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Worked solution

a) the associated magnetic field is given as
Exemplar Solutions Class 12 Physics Chapter 8 - 15

b) the electromagnetic field can be written in terms of the associated magnetic field as
Exemplar Solutions Class 12 Physics Chapter 8 - 16

c)
Exemplar Solutions Class 12 Physics Chapter 8 - 17

Q8.10Written answer

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

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Worked solution

b) Ey, Bz

d) Ez, By