# MCQ Questions for Class 12 Physics Chapter 8 Electromagnetic Waves with Answers

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## Electromagnetic Waves Class 12 MCQs Questions with Answers

Question 1.
Which of the following has the lowest frequency.
(a) Infraredrays
(b) X-rays
(c) UV rays
(d) γ-rays

Question 2.
The frequency of visible light is of the order of.
(a) 1012 Hz
(b) 1015 Hz
(c) 108 Hz
(d) 1018 Hz

Question 3.
The speed of electromagnetic waves in a medium is:
(a) $$\frac {1}{\sqrt{µE}}$$
(b) $$\frac {1}{\sqrt{µ_0ε_0}}$$
(c) $$\sqrt{\frac {µ}{ε}}$$
(d) $$\frac {1}{µE}$$

Answer: (a) $$\frac {1}{\sqrt{µE}}$$

Question 4.
Which of the following waves are used in telecommunication.
(a) visible light
(b) microwaves
(c) ultraviolet
(d) infrared

Question 5.
The displacement current flows in the dielectric of the capacitor, when the potential difference across its plates:
(a) changes (increases/decreases) with time.
(b) changes with distance.
(c) attains a constant value.
(d) None of these.

Answer: (a) changes (increases/decreases) with time.

Question 6.
The physical properties shared by both radiowaves and sound waves are:
(i) both can be polarised.
(ii) both can be reflected.
(iii) both can be diffracted.
(a) if (i), (ii), (iii) all are correct.
(b) if (ii), (iii) are correct.
(c) if only (i) is correct.
(d) None of these.

Answer: (b) if (ii), (iii) are correct.

Question 7.
The wavelength of X-rays is of the order of:
(a) 1 cm
(b) 1 angstrom
(c) 1 micron
(d) 1 m

Question 8.
Normal light is due to:
(a) electric field oscillations.
(b) magnetic field oscillations.
(c) oscillations of electric and magnetic fields in mutually perpendicular directions.
(d) None.

Answer: (c) oscillations of electric and magnetic fields in mutually perpendicular directions.

Question 9.
The strong radiation emitted in an electrical arc is:
(c) y-rays
(d) X-rays

Question 10.
Which of the following statement is incorrect.
(a) X-rays have minimum ionising power.
(b) α-rays have maximum ionizing power.
(c) ß-rays have maximum penetrating power.
(d) α-rays haye more penetrating power than a-rays.

Answer: (c) ß-rays have maximum penetrating power.

Question 11.
The wavelength of infrared rays is:
(a) less than that of visible light.
(b) greater than, that of visible light.
(c) greater or lesser depending on the source.
(d) None of these.

Answer: (b) greater than, that of visible light.

Question 12.
Which one of the following is used to defect infrared radiation:
(a) spectrometer
(b) pyrometer
(c) cloud chamber
(d) bolometer.

Question 13.
Displacement current is-the same as:
(a) r.m.s. current
(b) conduction current
(c) peak current
(d) None of these.

Question 14.
Microwaves have wavelength range:
(a) 0.1 gm to 0.7 gm
(b) 1 mm to 1 m
(c) 0.7 gm to 1 mm
(d) None of these.

Answer: (b) 1 mm to 1 m

Question 15.
The direction of $$\vec{E}$$ × $$\vec{B}$$ in an electromagnetic wave is
(a) same as that of $$\vec{E}$$
(b) same as that of $$\vec{B}$$
(c) same as the direction of propagation of electromagnetic wave.
(d) None of these.

Answer: (c) same as the direction of propagation of electromagnetic wave.

Fill in the Blanks

Question 1.
The varying electric field between the plates of the capacitor gives rise to ………………… and hence ………………… is also produced.

Question 2.
………………… produces magnetic field in the same way as does the conduction current.

Question 3.
………………… are transverse in nature.

Question 4.
………………… is responsible for the optical effects due to an electromagnetic radiation and hence it is also called as …………………

Question 5.
The ratio W/C is also called as the magnitude of ………………… for an electromagnetic wave.

Question 6.
………………… of electromagnetic waves is their inherent characteristic and does not change when it travels from one medium into another but its ………………… changes.

Question 7.
………………… produces heat when absorbed by the matter and ………………… are used in radio astronomy and radar system.

Question 8.
When allowed to fall on matter, ………………… rays produce an increase in temperature.

Question 9.
………………… are used for producing dehydrated fruits.

Question 10.
………………… and ………………… cause flourescence in certain substances.

Question 11.
………………… rays have higher penetrating power and small …………………

Question 12.
………………… helps to keep the earth’s atmosphere warm by preventing the escape of ………………… from the earth’s surface and traps them.

Question 13.
The ………………… is the main source of electromagnetic radiation.

Question 14.
……………….. layer absorbs most of the UV radiation and other harmful radiations of lower wave lengths.

Question 15.
The ozone layer converts ………………… radiation to infra-red.

Question 16
………………… rays are of nuclear origin while X-rays are of …………………

Question 17
……………….. are produced when a target of an element having high atomic number is bombarded by fast moving electrons.