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Electromagnetic Waves Class 12 MCQs Questions with Answers
Which of the following laws was modified by Maxwell by introducing the displacement current?
(a) Gauss’s law
(b) Ampere’s law
(c) Biot-Savart’s law
(d).None of these
Answer: (b) Ampere’s law
Electromagnetic waves have a speed of
(a) 3 × 105 kms-1
(b)3 × 106 kms-1
(c) 3 × 107 kms-1
(d) 3 × 108 kms-1
Answer: (a) 3 × 105 kms-1
Which of the following EMW has highest wavelength?
(a) X-ray
(b) ultraviolet rays
(c) infrared rays
(d) microwaves
Answer: (c) infrared rays
Who first demonstrated the existence of em waves?
(a) Hertz
(b) Maxwell
(c) Ampere
(d) Faraday
Answer: (a) Hertz
An EMW of v = 3 MHz passes from vacuum into dielectric medium with permittivity Er = 4, then
(a) Wavelength is doubled and the frequency remains unchanged
(b) Wavelength is doubled and the frequency become half
(c) Wavelength is halved and the frequency remains unchanged
(d) Wavelength and frequency both remain unchanged
Answer: (c) Wavelength is halved and the frequency remains unchanged
The conduction current is same as displacement current when source is
(a) ac only
(b) dc only
(c) either ac or dc
(d) neither dc nor ac
Answer: (c) either ac or dc
The ultra high frequency band of radio waves in electromagnetic wave is used as in
(a) television waves
(b) cellular phone communication
(c) commercial FM radio
(d) both (a) and (c)
Answer: (b) cellular phone communication
If ue and um arc the electric and magnetic field densities in an electromagnetic wave, then (c is the speed of light)
(a) ue = um
(b) ue = cum
(c) ue = um/c
(d) None of these
Answer: (a) ue = um
Light Year is the unit of
(a) distance
(b) time
(c) energy
(d) intensity of light
Answer: (a) distance
Which of the following electromagnetic waves is used in medicine to destroy cancer cells?
(a) IR-rays
(b) Visible rays
(c) Gamma rays
(d) Ultraviolet rays
Answer: (c) Gamma rays
Which basic oscillatory circuit is used these days to produce electromagnetic waves?
(a) LC oscillatory circuit
(b) LCR circuit
(c) Inductive circuit
(d) Capacitive circuit
Answer: (a) LC oscillatory circuit
Choose the wave relevant to telecommunication
(a) ultraviolet
(b) infrared
(c) microwave
(d) visible light
Answer: (c) microwave
Displacement current is always
(a) equal to conduction current
(b) less than conduction current
(c) greater than conduction current
(d) the sum of current due to flow of positive and negative ions
Answer: (a) equal to conduction current
The dimensions of E/Bare same as that of
(a) charge
(b) current
(c) velocity
(d) acceleration
Answer: (c) velocity
An EMW of v = 3 MHz passes from vacuum into dielectric medium with permittivity Er = 4, then
(a) Wavelength is doubled and the frequency remains unchanged
(b) Wavelength is doubled and the frequency become half
(c) Wavelength is halved and the frequency remains unchanged
(d) Wavelength and frequency both remain unchanged
Answer: (c) Wavelength is halved and the frequency remains unchanged
Frequency of a wave is 6 × 1015. Hz. The wave is
(a) Radiowave
(b) Microwave
(c) X-ray
(d) Ultra violet
Answer: (d) Ultra violet
Solar radiation is
(a) transverse EMW
(b) longitudinal EMW
(c) both (a) and (b)
(d) None of these
Answer: (a) transverse EMW
What physical quantity is the same for X-rays of wavelength 10-10 m, red light of wavelength 680 nm and radio waves of wavelength 500 m?
(a) Wavelength
(b) Frequency
(c) Speed
(d) None of these.
Answer: (c) Speed
What is the ratio of the speed of infrared and ultraviolet rays in a vacuum?
(a) 1:5
(b) 2:1
(c) 1
(d) 0
Answer: (c) 1
If a variable frequency ac source is connected to a capacitor then with decrease in frequency the displacement current will
(a) increase
(b) decrease
(c) remains constant
(d) first decrease then increase
Answer: (b) decrease
A charged particle oscillates about its mean equilibrium position with a frequency of 109 Hz. The frequency of electromagnetic waves produced by the oscillator is
(a) 106 Hz
(b) 107 Hz
(c) 108 Hz
(d) 109 Hz
Answer: (d) 109 Hz
The waves used by artificial satellites for communication is
(a) microwaves
(b) infrared waves
(c) radio waves
(d) X-rays
Answer: (a) microwaves
Displacement current is due to
(a) the flow of electrons
(b) the Varying electric field
(c) the ionization of atmosphere
(d) the flow of protons
Answer: (b) the Varying electric field
EMW are produced by
(a) charge in uniform motion only
(b) charge at rest only
(c) accelerated or decelerated charge only
(d) all of the above
Answer: (c) accelerated or decelerated charge only
Name the law which states that a varying electric field produces a magnetic field
(a) Biot-Savart’s law
(b) Faraday’s law
(c) Modified Ampere’s law
(d) None of these
Answer: (c) Modified Ampere’s law
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