# Physics class 12 chapter 8 Objective Questions

## Electromagnetic Waves Objective

1. Maxwell in his famous equations of electromagnetism introduced the concept of

(a) ac current

(b) displacement current

(c) impedance

(d) reactance

Answer: (b) displacement current

1. 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

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

1. 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)

Answer: (d) both (b) and (c)

1. 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.

Answer: (c) Both electric and magnetic field vectors are parallel to each other and perpendicular to the direction of propagation of wave.

1. 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

Answer: (a) Both magnetic and electric fields

1. A charged particle oscillates about its mean equilibrium position with a frequency of 109 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

1. 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

1. The waves used by artificial satellites for communication is

(a) microwaves

(b) infrared waves

(d) X-rays

1. 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

1. Which has the longest wavelength?

(B) X-rays

(C) Ultraviolet rays

(D) Infrared

1. Which of the following has a minimum wavelength?

(A) X-Rays

(B) Y-Rays

(C) Micro Wave

1. The frequency range of microwaves (in hertz) is

(A) 3 × 108 – 4 x 104

(B) 7.5 x 104 – 3.8 x 1011

(C) 3 x 1021 – 3 x 1018

(D) 3 x 1012 – 3 x 1010

Answer: (D) 3 x 1012 – 3 x 1010

1. Wavelength range in meter for green light is

(A) 4x 10-7– 4.5 x 10-7

(B) 4.5 x 10-7 – 5 x 10-7

(C) 5 x 10-7 – 5.7 x 10-7

(D) None of these

Answer: (C) 5 x 10-7 – 5.7 x 10-7

1. According to the law of electromagnetism, the speed of electromagnetism in all the inertial frames is

(A) Same

(B) different

(C) not definite

(D) None of these.

1. Maxwell equations represent four laws of electromagnetism. Maxwell Ampere law relates

(A) The rate of change of magnetic flux to total current

(B) The rate of change of magnetic flux to displacement current

(C) the rate of change of magnetic flux to current

(D) None of these

Answer: (A) The rate of change of magnetic flux to total current

1. Unit of displacement current is

(A) A

(B) AM

(C) Om/A

(D) I

1. Which of the following are used to make labs free from bacteria?

(A) UV rays

(B) IR rays

(C) X-rays

(D) none

Answer: (A) UV rays

1. The propagation of the electromagnetic wave is along

(A) normal to electric field only

(B) normal to magnetic field only

(C) normal to both the electric, and magnetic field

(D) None of these

Answer: (C) normal to both the electric, and magnetic field

1. Which is a wrong statement?

(A) Electromagnetic waves are transverse

(B) Electromagnetic waves travel in a vacuum at the speed of light

(C) The speed of the electromagnetic wave is the same in all media

(D) Electromagnetic waves are emitted by accelerated charges

Answer: (C) The speed of the electromagnetic wave is the same in all media

1. The water molecule in foods have a rotational frequency in the range of

(A) ultraviolet waves

(B) infrared waves

(C) microwaves

(D) visible waves

1. The frequency of the microwave is

(A) less than that of radiowaves

(B) more than that of radiowaves para

(C) more than that of light waves

(D) less than the range of audible waves

Answer: (B) more than that of radiowaves para

1. Which of the following is not shown by electromagnetic waves?

(A) reflection

(B) polarization

(C) diffraction

(D) None of these

Answer:  (D) None of these

1. The energy of electromagnetic radiation is 13.2 keV. This radiation is related to which region of the spectrum ?

(A) Visible

(B) X-rays

(C) Ultra violet

(D) Infrared