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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
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) \(\frac {1}{\sqrt{µE}}\)
(b) \(\frac {1}{\sqrt{µ_0ε_0}}\)
(c) \(\sqrt{\frac {µ}{ε}}\)
(d) \(\frac {1}{µE}\)
Answer
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
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
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
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 \(\vec{E}\) × \(\vec{B}\) 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
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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