Electromagnetic Waves

Electromagnetic Waves Class 12 Physics MCQs

1. Maxwell in his famous equations of electromagnetism introduced the concept of
(a) ac current
(b) displacement current
(c) impedance
(d) reactance

2. 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

3. 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

4. An electromagnetic wave can be produced, when charge is
(a) moving with a constant velocity
(b) moving in a circular orbit
(c) falling in an electric field
(d) both (b) and (c)

5. Which of the following statement is false for the properties of electromagnetic waves?
(a) Both electric and magnetic field vectors attain the maxima and minima at the same place and same time.
(b) The energy in electromagnetic waves is divided equally between electric and magnetic field vectors.
(c) Both electric and magnetic field vectors are parallel to each other and perpendicular to the direction of propagation of wave.
(d) These waves do not require any material medium for propagation.

6. Which of the following has/have zero average value in a plane electromagnetic wave?
(a) Both magnetic and electric fields
(b) Electric field only
(c) Magnetic field only
(d) None of these

7. 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

8. If E and B denote electric and magnetic fields respectively, which of the following is dimensionless?

9. 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)

10. The waves used by artificial satellites for communication is
(a) microwaves
(b) infrared waves
(c) radio waves
(d) X-rays

11. 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

Question 12.
The dimensional formula of \(\vec{E}\) is:
(a)[MLT^-2A^-1]
(b) [MLT^-3A^-1]
(c) [MLT^-2A^-2]
(d) None of these

Question 13.
The dimensional formula of is:
(a) [MLT^-2A^-1]
(b) [ML⁰T^-2A^-1]
(c) [ML⁰T^-3A^-1]
(d) None of these

Question 14.
Which of the following has the dimensions of current?
(a) ε₀ \(\vec{E}\).\(\vec{dt}\)
(b) µ₀ \(\vec{E}\).\(\vec{dt}\)
(c) \(\frac{\vec{B}.\vec{dl}}{µ_0}\)
(d) \(\frac{\vec{B}.\vec{dl}}{ε_0}\)

Question 15.
Which of the following has the dimensions of charge?
(a) \(\frac{ε_0\vec{E}}{\vec{ds}}\)
(b) µ₀ \(\vec{E}\).\(\vec{ds}\)
(c) \(\frac{ε_0}{µ_0}\) \(\vec{E}\).\(\vec{ds}\)
(d) \(\frac{µ_0}{ε_0}\) \(\vec{E}\).\(\vec{ds}\)

Question 16.
Maxwell’s equation involving \(\frac{d}{dt}\) \(\vec{B}\) is obtained-from:
(a) Ampere’s law
(b) Gauss’s law
(c) Faraday’s law
(d) Biot-Savart’s law

Question 17.
The dimensions of \(\vec{E}\), \(\vec{dl}\) are identical to that of:
(a) potential
(b) charge
(c) current
(d) None of these

Question 18.
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

Question 19.
Choose the wave relevant to telecommunication :
(a) ultraviolet
(b) infrared
(c) microwave
(d) visible light

Question 20.
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

Question 21.
Which of the following EMW has highest wavelength?
(a) X-ray
(b) ultraviolet rays
(c) infrared rays
(d) microwaves

Question 22.
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

Question 23.
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

Question 24.
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

Question 25.
Who first demonstrated the existence of em waves?
(a) Hertz
(b) Maxwell
(c) Ampere
(d) Faraday

Question 26.
If \(\vec{B}\) is the magnetic field vector and \(\vec{E}\) is the electric field vector in an em wave, then which of the following relations is correct? Here c is the speed of fight:
(a) c = \(\frac{E}{B}\)
(b) c = BE
(c) c = \(\frac{B}{E}\)
(d) c = \(\frac{1}{EB}\)

Question 27.
The dimensions of E/Bare same as that of:
(a) charge
(b) current
(c) velocity
(d) acceleration

Question 28.
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

Question 29.
The existence of EMW was experimentally established by :
(a) Sir S. C. Bose
(b) Maxwell
(c) Marconi
(d) Hertz

Question 30.
An EMW of v = 3 MHz passes from vacuum into dielectric medium with permittivity E_r = 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

Question 31.
Frequency of a wave is 6 × 10¹⁵. Hz. The wave is :
(a) Radiowave
(b) Microwave
(c) X-ray
(d) Ultra violet

Question 32.
Choose the wrong statement?
(a) Electromagnetic waves are transverse
(b) Electromagnetic waves travel with the speed of light in free space
(c) Electromagnetic waves are produced by accelerating charges
(d) Electromagnetic waves travel with the same speed in all media

Question 33.
If u_e and u_m arc the electric and magnetic field densities in an electromagnetic wave, then (c is the speed of light):
(a) u_e = u_m
(b) u_e = c u_m
(c) u_e = \(\frac{u_m}{c}\)
(d) None of these

Question 34.
Solar radiation is :
(a) transverse EMW
(b) longitudinal EMW
(c) both (a) and (b)
(d) None of these

Question 35.
Ampere’s circuital law was modified by:
(a) Laplace
(b) Gauss
(c) Maxwell
(d) Hertz

Question 36.
Light Year is the unit of:
(a) distance
(b) time
(c) energy
(d) intensity of light