Physics class 12 chapter 8 Objective Questions

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

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

Answer: (c) either ac or dc

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

Answer: (b) decrease

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)

Answer: (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.

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

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

Answer: (a) Both magnetic and electric fields

7. 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

8. 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

9. The waves used by artificial satellites for communication is

(a) microwaves

(b) infrared waves

(c) radio waves

(d) X-rays

Answer: (a) microwaves

10. 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

11. Which has the longest wavelength? 

(A) Radio waves

(B) X-rays

(C) Ultraviolet rays

(D) Infrared 

Answer: (A) Radio waves

12. Which of the following has a minimum wavelength? 

(A) X-Rays 

(B) Y-Rays

(C) Micro Wave

(D) Radio wave Answer: (B) Y-Rays

13. 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

14. 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

15. 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.

Answer: (A) Same 

16. 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

17. Unit of displacement current is 

(A) A

(B) AM

(C) Om/A

(D) I

Answer: (A) A

18. 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 

19. 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

20. 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

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

(A) ultraviolet waves

(B) infrared waves 

(C) microwaves

(D) visible waves

Answer: (C) microwaves

22. 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

23. 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

24. 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 

Answer: (B) X-rays