Class 12th Physics Objective Question and Answer Electromagnetic Waves

Class 12th Physics Objective Question and Answer Electromagnetic Waves
Class 12th Physics Objective Question and Answer Electromagnetic Waves

Physics MCQs for Class 12 with Answers Chapter 8 Electromagnetic Waves

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Class 12th Physics Objective Question and Answer Electromagnetic Waves

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

Answer

Answer: (a) Infraredrays


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

Answer

Answer: (b) 1015 Hz


Question 3.
The speed of electromagnetic waves in a medium is:
(a) 1µE
(b) 1µ0ε0
(c) µε−−√
(d) 1µE

Answer

Answer: (a) 1µE


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

Answer

Answer: (b) microwaves


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

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

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

Answer

Answer: (b) 1 angstrom


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

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


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

Answer

Answer: (b) Ultraviolet radiation


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

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

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.

Answer

Answer: (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.

Answer

Answer: (b) conduction current


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

Answer: (b) 1 mm to 1 m


Question 15.
The direction of E⃗  × B⃗  in an electromagnetic wave is
(a) same as that of E⃗ 
(b) same as that of B⃗ 
(c) same as the direction of propagation of electromagnetic wave.
(d) None of these.

Answer

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.

Answer

Answer: Displacement current, magnetic field.


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

Answer

Answer: Displacement current.


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

Answer

Answer: Electromagnetic waves.


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

Answer

Answer: Electric vector, light vector.


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

Answer

Answer: Propagation vector (k).


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

Answer

Answer: Frequency, wavelength.


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

Answer

Answer: Microwaves, radiowaves.


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

Answer

Answer: infrared.


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

Answer

Answer: Infrared rays.


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

Answer

Answer: Ultra-violet rays and X-rays.


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

Answer

Answer: Gamma, ionising power.


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

Answer

Answer: Ozone layer, infrared rays.


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

Answer

Answer: Sun.


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

Answer

Answer: Ozone layer.


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

Answer

Answer: Ultraviolet (UV).


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

Answer

Answer: Gamma, atomic origin.


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

Answer

Answer: X-rays.


Question 18.
The frequency range of music or speech is …………………

Answer

Answer: 20 Hz to 20 KHz.

 

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