NCERT Solutions for class 12 Physics | Chapter 8 - Electromagnetic Waves

Questions
1 A plane electromagnetic wave is incident on a material surface. 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

Answer:p ≠ 0, E = 0
2 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

Answer:in phase and perpendicular to each other
3 The electromagnetic wave used to treat muscular pain is:
A VHF radiowaves
B X-rays
C Ultraviolet rays
D Infrared radiations

Answer:Infrared radiations
4 A beam of light travelling along x-axis is described by the magnetic field Bz = 5 X 10-7T sinω(t – x/c) If a beam of alpha particle moves in this filed along y – axis with a speed of 3 X 107 m/s, then the maximum electric and magnetic forces experienced by it will be:
A 4.80 X 10-10N and 4.8 X 10-12N respectively.
B 4.80 X 10-17N and 4.8 X 10-18N respectively.
C 2.80 X 10-5N and 2.1 X 10-7N respectively.
D 1.5 X 10-5N and 4.1 X 10-7N respectively.

Answer:4.80 X 10-17N and 4.8 X 10-18N respectively.
5 An electromagnetic wave propagating along north has its electric field vector upwards. Its magnetic field vector point towards
A north
B east
C west
D downwards

Answer:east
6 According to Maxwell’s hypothesis, a changing electric field gives rise to
A an e.m.f
B electric displacement current
C magnetic field
D pressure gradient

Answer:magnetic field
7 Which of the following has/have zero average value in a plane electromagnetic wave?
A Both magnetic and electric field
B Electric field only
C Magnetic energy
D Electric energy

Answer:Both magnetic and electric field
8 Select the wrong statement. EM waves
A are transverse in nature.
B travel in free space at a speed of light.
C are produced by accelerating charges.
D travel in all media with same speed.

Answer:travel in all media with same speed.
9 An electron oscillating with a frequency of 3 × 106 Hz, would generate
A X-rays
B ultraviolet rays
C radio waves
D microwaves

Answer:radio waves
10 Displacement current goes through the gap between the plates of a capacitor when the charge on the capacitor
A is changing with time
B decreases
C does not change
D decreases to zero

Answer:is changing with time
11 If a variable frequency ac source connected to a capacitor then with decrease in frequency, the displacement current will
A increase
B decrease
C remain constant
D first decrease then increase

Answer:decrease
12 The current in the electric circuit which arises due to flow of electrons in the connecting wires of the circuit in a defined closed path is called
A alternating current
B direct current
C conduction current
D displacement current

Answer:conduction current
13 The polarisation of electromagnetic wave is in
A the directions of electric and magnetic field
B the directions of electric field
C the direction of magnetic field
D can not be polarized

Answer:the directions of electric field
14 The electromagnetic waves do not transport
A energy
B charge
C momentum
D information

Answer:charge
15 The electromagnetic radiation used in food processing sterilizing agent is
A microwaves
B UV rays
C gamma rays
D radio waves

Answer:UV rays
16 The waves used in telecommunication are
A IR
B UV
C Microwave
D Cosmic rays

Answer:Microwave
17 What is the cause of “Green house effect”?
A Infrared rays
B Ultraviolet rays
C X-rays
D Radio waves

Answer:Infrared rays
18 Radio waves do not penetrate in the band of
A ionosphere
B mesosphere
C troposphere
D stratosphere

Answer:ionosphere
19 The wavelength of X-ray is of the order of
A 1 metre
B 1 cm
C 1 micron
D 1 angstrom

Answer:1 angstrom
20 The range of wavelength of visible light is
A 50 Å to 500 Å
B 4000 Å to 8000 Å
C 9000 Å to 25,000 Å
D 15,000 Å to 25,000 Å

Answer:4000 Å to 8000 Å

Chapters

junior administrative assistant jaa test series