Electromagnetic Wave

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1.Why is the quantity e0 dFE/dt called the displacement current?

2. Using a d.c. source, a capacitor has been fully charged. What are the magnitudes of conduction and displacement currents?

3. What is the ratio of speed of infrared and ultraviolet rays in vacuum?

4. An electromagnetic wave consists of oscillating electric and magnetic fields. What is the phase relationship between these oscillations?

5. Radio waves diffract predominately around building while light waves, which are also electromagnetic waves, do not. Why?

6. Electromagnetic waves with wavelength
(i) l1 are used to treat muscular strain.
(ii) l2 are used by a FM radio station for broadcasting
(iii) l3 are used to detect fracture in bones
(iv) l4 are absorbed by the ozone layer of the atmosphere.
Identify and name the part of electromagnetic spectrum to which these radiations belong. .Arrange these wavelengths in decreasing order of magnitude.

7. (a) Which of the following, if any, can act as a source of electromagnetic waves?
(i) A charge moving with a constant velocity.
(ii) A charge moving in a circular orbit.
(iii) A charge at rest.
Give reason. (b) Identify the part of the electromagnetic spectrum to which waves of frequency (i) 1020 Hz (ii)109 Hz belong to microwaves.

8)If the area of the TV telecast is to be doubled then what will be the height of the transmitting antenna ?.

9.Which of the physical quantity is NOT transported by the em waves?

10.What happens to the average temperature on the surface of the earth if there is no atmosphere?.

11. Mention the law, that which asserts that the electric field lines cannot form close loops?

12.What are the characteristics properties of electromagnetic waves?

13.The energy of the electromagnetic wave is in the order of 15KV . To which part of the spectrum does it belong?

14. Name em waves are used in telecommunication

15.what is condition for obtaining displacement current between the plate of the capacitor?

16.Mention the pair of space and time varying E and B fields which would generate a plane em wave travelling in the z-direction? Ex and By

17. A plane electromagnetic wave travels, in vacuum, along the y-direction. Write (i) the ratio of the magnitude, and (ii) the directions of its electric and magnetic field vectors. (ii) For an electromagnetic wave traveling along y-diretion, its electric and magnetic field vectors are along z-axis and x-axis respectively. The direction of E→ ×  B→ ´ is same as that of direction of wave propagation and kˆ ´ iˆ = ˆj .

18. Suppose that the electric field amplitude of an electromagnetic wave is E0=120 NC-1 and that its frequency is v=50.0 MHz. (a) Determine, B0, w,k and l. (b) Find expressions for E and B.

19. Answer the following questions:
(a) Long distance radio broadcasts use short-wave bands. Why?
(b) It is necessary to use satellite for long distance TV transmission. Why?
(c) Optical and radio telescopes are built on the ground but X-ray astronomy is possible only from satellites orbiting the earth. Why?
(d) If the earth did not have an atmosphere, would its average surface temperature be higher or lower than what it is now?


CBSE Physics (Chapter Wise With Hint / Solution) Class XII (By Mr. Sreekumaran Nair)