Daily Practice Problems
Class 12 Physics
Electromagnetic Waves Question 1:

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 (b)

Question 2:

Which of the following radiations are used to treat muscle ache?

(a) Microwaves

(b) Infrared Rays

(c) Ultraviolet Rays

(d) X-Rays

Question 3:

The correct ascending order for the frequencies of below electromagnetic radiation is

(a) Gamma Rays, X-rays, Microwave, Radiowave

(b) Gamma Rays, Microwave, X-rays, Radiowave

(c) Gamma Rays, Radiowave, Microwave, X-rays,

(d) Radiowave, Microwave, X-rays, Gamma Rays

Question 4:

The current carried by conductors due to flow of charges is __________.

(a) conduction Current

(b) displacement Current

(c) both

(d) none of these

Question 5:

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

Question 6:

A plane electromagnetic wave of frequency 25 MHz travels in free space along the x-direction. At a particular point in space and time, E = 6.3 ˆj V/m. What is B at this point?

Question 7:

Light with an energy flux of 18 W/cm2 falls on a non-reflecting surface at normal incidence. If the surface has an area of 20 cm2, find the average force exerted on the surface during a 30-minute time span.

Question 8:

Why infrared rays are often called as heat waves?

Question 9:

Sky waves are not used in transmitting TV signals. Why? Suggest two methods by which range of TV transmission can be increased?

Question 10:

Name the types of EM radiations which

1. are used in destroying cancer cells,

2. cause tanning of the skin and

3. maintain the earth’s warmth.

Write briefly a method of producing any one of these waves.

Question 11:

The magnetic field in a plane electromagnetic wave is given by By= (2 × 10–7) T sin (0.5×103x+1.5×1011t).

(a) What is the wavelength and frequency of the wave?

(b) Write an expression for the electric field.

Question 12:

Calculate the electric and magnetic fields produced by the radiation coming from a 100 W bulb at a distance of 3 m. Assume that the efficiency of the bulb is 2.5% and it is a point source.

Question 13:

How we can say that infrared radiation plays an important role in maintain the earth’s warmth?

Question 14:

(a) If the earth did not have atmosphere, would its average surface temperature be higher or lower than what it is now? Explain.

(b) An EM wave exerts pressure on the surface on which it is incident. Justify.?

Question 15:

What is Green House effect?

Question 16:

How are microwaves produced? Why is it necessary in microwave ovens to select the frequency of microwaves to match the resonant frequency of water molecules?

Question 17:

In a plane electromagnetic wave, the electric field oscillates sinusoidally at a frequency of 4.0 × 1010 Hz and amplitude 48 V m–1. What is the maximum magnetic energy density of electromagnetic field?

Question 18:

How can radio waves generated? What are the uses of radio waves?

Question 19:

Electromagnetic waves travel in a medium at a speed of 2 × 108 m/s. the relative permeability of the medium is 1.0. calculate the relative permittivity.

Question 20:

The intensity of the sunlight reaching the earth is 1380 Wm-2. Calculate the amplitude of electric and magnetic field in the light wave. Assume the light to be a plane monochromatic wave.

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