CBSE Class 12 Physics Chapter-8 Important Questions – Free PDF Download
Free PDF download of Important Questions with Answers for CBSE Class 12 Physics Chapter 8 – Electromagnetic Waves 2 Marks Questions prepared by expert Physics teachers from latest edition of CBSE(NCERT) books only by CoolGyan to score more marks in CBSE board examination.
CBSE Class 12 Physics Chapter-8 – Electromagnetic Waves
CBSE Class 12 Physics Important Questions Chapter 8 – Electromagnetic Waves
2 Marks Questions
1. Write the application of Infra-red radiations?
Ans. (1) infra-red radiations are used to take photographs under foggy conditions.
(2) Infra-red radiations are used in revealing the secret writings on the ancient walls.
2. Which constituent radiation of the electromagnetic spectrum is used?
(1) To photograph internal parts of human body.
(2) For air aircraft navigation
Ans. (1) X -Rays
(2) Microwaves
3. Electric field in a plane electromagnetic wave is given by
(a) Write an expression for the magnetic field
(b) What is the magnitude of wavelength and frequency of the wave?
Ans. (a) 
Since magnetic field and electric field are 
to each other
—-(1)
Compare e.g. (1) with standard equation
By = BO sin 
4. IF the earth did not have atmosphere would its average surface temperature be higher or lower than what it is now?
Ans. The infra-red radiations get trapped inside the earth’s atmosphere due to green house effect which makes the earth warm. Therefore average temperature of the earth would have been low.
5. Sky waves are not used in transmitting TV signals, Why? Suggest two methods by which range of TV transmission can be increased?
Ans. Sky waves are not used in transmitting TV signals as they are not reflected by the ionosphere.
Methods of increasing range of TV transmission
(1) Tall antenna
(2) Geostationary satellites
6. “Greater the height of a TV transmitting antenna, greater is its coverage.” Explain.
Ans. Since d = 
If height is increased distance upto which TV coverage can be done will increases.
7. A plane electromagnetic wave travels in vacuum along z-direction. What can you say about the directions of its electric and magnetic field vectors? If the frequency of the wave is 30 MHz, what is its wavelength?
Ans. The electromagnetic wave travels in a vacuum along the z-direction. The electric field (E) and the magnetic field (H) are in the x–y plane. They are mutually perpendicular.
Frequency of the wave, 
= 30 MHz = 
Speed of light in a vacuum, c = 
m/s
Wavelength of a wave is given as:
8. A radio can tune in to any station in the 7.5 MHz to 12 MHz band. What is the corresponding wavelength band?
Ans. A radio can tune to minimum frequency, 
= 7.5 MHz=
Maximum frequency, 
= 12 MHz = 
Speed of light, c = m/s
Corresponding wavelength for can be calculated as:
Corresponding wavelength for v
can be calculated as:
Thus, the wavelength band of the radio is 40 m to 25 m.
9. A charged particle oscillates about its mean equilibrium position with a frequency of 
Hz. What is the frequency of the electromagnetic waves produced by the oscillator?
Ans. The frequency of an electromagnetic wave produced by the oscillator is the same as that of a charged particle oscillating about its mean position i.e., 
Hz.
10. The amplitude of the magnetic field part of a harmonic electromagnetic wave in vacuum is 
= 510 nT. What is the amplitude of the electric field part of the wave?
Ans. Amplitude of magnetic field of an electromagnetic wave in a vacuum,
B0 = 510 nT =
Speed of light in a vacuum, c =
Amplitude of electric field of the electromagnetic wave is given by the relation,
E 
=
= 153 N/C
Therefore, the electric field part of the wave is 153 N/C.