PHYSICS-XII
TEST 14- UNIT- ELECROMAGNETIC WAVE
MM-25 Time-50 Min
All questions are compulsory. b) Questions 1 to 10 are one mark questions. c) Questions 11 to 13 are two
marks questions. d) Questions 14 to 16 are three marks questions
1. What is the phase difference between electric and magnetic fields in an electromagnetic wave?
(a) 0 (b) π (c) π/2 (d) π/4
2 Which of the following waves have a maximum frequency?
a. infrared waves
b. gamma rays
c. microwaves
d. radio waves
3. Which of the following is used to investigate the structure of solids?
a. Gamma Rays
b. Infrared Rays
c. X-Rays
d. Cosmic Rays
4. Which of the following radiations are used to treat muscle ache?
a. Microwaves
b. Infrared Rays
c. Ultraviolet Rays
d. X-Rays
5. When is the conduction current the same as the displacement current?
a. When the source is ac
b. When the source is dc
c. When the source is either an ac or a dc
d. When the source is neither dc nor ac
6. An electromagnetic wave can be produced when the charge is
a. moving in a circular orbit
b. moving with a constant velocity
c. falling in an electric field
d. Both (a) and (c)
7. The ratio of contributions made by the magnetic field and electric field components to the intensity
of an EM wave is
a. 1:1 b. c:1 c. c2:1 d . √c:1
8. Write modified amperes circuital law
9. What is expression for displacement current
10. Draw formula for refractive index in tems of µ & €
SECTION B
11. 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?
12. The amplitude of the magnetic field part of a harmonic electromagnetic wave in vacuum is B0 = 510
nT. What is the amplitude of the electric field part of the wave?
13. Suppose that the electric field amplitude of an electromagnetic wave is E0 = 120 N/C and that its
frequency is ν = 50.0 MHz. (a) Determine, B0, ω, k, and λ. (b) Find expressions for E and B.
SECTION C
14. In a plane electromagnetic wave, the electric field oscillates sinusoidally at a frequency of 2.0 × 1010
Hz and amplitude 48 V m−1.
(a) What is the wavelength of the wave?
(b) What is the amplitude of the oscillating magnetic field?
(c) Show that the average energy density of the E field equals the average energy density of the B field. [c =
3 × 108 m s−1.]
15. Suppose that the electric field part of an electromagnetic wave in vacuum is E = {(3.1 N/C) cos [(1.8
rad/m) y + (5.4 × 106 rad/s)t]} .
(a) What is the direction of propagation?
(b) What is the wavelength λ?
(c) What is the frequency ν?
(d) What is the amplitude of the magnetic field part of the wave?
(e) Write an expression for the magnetic field part of the wave.
16.About 5% of the power of a 100 W light bulb is converted to visible radiation. What is the average
intensity of visible radiation
(a) at a distance of 1 m from the bulb?
(b) at a distance of 10 m?
