CBSE Class 12 Physics Electromagnetic Waves Notes Set B

11. A variable frequency a.c source is connected to a capacitor. Will the displacement current increase or decrease with increasing frequency?

Ans Increases

12. EMW travel in a medium at a speed of 2x10⁸ m/s. the relative permeability of the medium is 1.0. Calculate the relative permittivity?

Ans ε_r = 2.25 

14. How does a charge q oscillating at certain frequency produce electromagnetic wave?

Ans Oscillating charge produces oscillating E which produces oscillating B and so on

15. How would you establish an instantaneous displacement current of 1A in the space between the parallel plates of 1μF capacitor?

Ans By changing the voltage dv/dt =10⁶ V/s

16. Name the Maxwell’s equation among the four which shows that the magnetic monopole does not exist?

Ans Gauss’s theorem of Magnetism

17. Write the unit of μ_o ε_o? 

Ans (m/s)

18. Give reason for decrease or increase in velocity of light, when it moves from air to glass or glass to air respectively? 

Ans The velocity of light depends on ε & μ of the medium.

19. A parallel plate capacitor made of circular plates each of radius 10 cm has a capacitance 200pF. The capacitor is connected to a 200V a.c. supply with an angular frequency of 200 rad/s.

a) What is the rms value of conduction current

b) Is the conduction current equal to displacement current

c) Peak value of displacement current

d) Determine the amplitude of magnetic field at a point 2cm from the axis between the plates

Ans a) I_rms = 8μA

b) I_c = I_d

c) I_o =21/2 I_rms

B = 4.525 x 10^-12 T

20. Electromagnetic waves with wavelength

(i) λ , are used to treat muscular strain.

(ii)  λ , are used by a FM radio station for broadcasting..

(iii)  λ , are produced by bombarding metal target by high speed electrons.

(iv)  λ , are observed by the ozone layer of the atmosphere.

Identify and name the part of electromagnetic spectrum to which these radiation belong. Arrange these wave lengths, in decreasing order of magnitude.

21. a) Which of the following if any, can act as a source of electromagnetic waves.

(i) A charge moving with constant velocity.

(ii) A charge moving in circular orbit.

(iii)A charge at rest. Give reason

(b) Identify the part of electromagnetic spectrum to which the waves of frequency

(i) 1020 Hz (ii) 109 Hz belong.

Ans a) Can’t produce em waves because no accelration.

(ii) It is accelrated motion - can produce em waves.

(iii)Can’t produce em waves because no accelration.

b) (i) Gamma rays.

(ii) Micro waves

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