12th physics chapter 8 objective questions in English

1. Electromagnetic waves are produced by :

(A) A static charge

(b) A uniformly moving charge

(c) An accelerated charge

(d) Neutral particles

2. The displacement current exists in the gap between the plates of a capacitor when the charge on the capacitor :

(A) Is  increasing with time

(b) Is decreasing with time

(c) Becomes constant

(d) Is zero

3. A magnetic field can be produced by :

(A) A moving charge only

(b) A charging electric field only

(c) Both of these

(d) None of these

4. Which of the following has/have zero average value in a plane electromagnetic wave ?

(A) Electric field

(b) Magnetic field

(c) Electric energy

(d) Magnetic energy

5. In a plane electromagnetic wave the phase difference between electric and magnetic field vectors is :

(A) Zero

(b) π/4

(c) π/2

(d) π

6. When X-rays , y-rays and microwaves travel in vacuum have :

(A) Same wavelength but different speed

(b) Same frequency but different speed

(c) Same speed but different wave length

(d) Same speed and same frequency

7. Electromagnetic radiation is :

(A) ∝ – rays

(b) β – rays

(c) X – rays

(d) Positive rays

8. (μ₀ε₀)^-1/2 has the value equal to :

(A) 3 × 10⁸cm/s

(b) 3 × 10¹⁰cm/sec

(c) 3 × 10⁹cm/s

(d) 3 × 10⁸km/sec

9. Which of the following electromagnetic waves has the longest wavelength : (JAC , 2014)

(A) X – rays

(b) Ultra-violet rays

(c) Infra-red rays

(d) Micro waves

10. The wave of the highest frequency is : (JAC , 2015)

(A) Ultra-violet wave

(b) gamma-rays

(c) Visible light waves

(d) Radio waves

11. The ratio of the amplitudes of electric and magnetic field in an electromagnetic wave is : (JAC , 2014)

(A) √μ₀ε₀

(b) 1/√μ₀ε₀

(c) μ₀ε₀

(d) 1/μ₀ε₀

12. Heat radiations are :

(A) γ – rays

(b) Micro waves

(c) Infra-red radiations

(d) Radio waves

13. Electromagnetic radiation used in telecommunication is :

(A) Ultra-violet

(b) Infra-red

(c) Visible

(d) Micro wave

14. Electromagnetic waves having highest frequency are :

(A) ∝ – rays

(b) γ – rays

(c) Visible light

(d) Radio waves

15. Infra – red radiations are detected by :

(A) Spectrometer

(b) pyrometer

(c) nanometer

(d) photometer

16. Which of the following are not electromagnetic waves :

(A) Cosmic rays

(b) γ – rays

(c) β – rays

(d) ∝ – rays

17. The dimensions of (μ₀ε₀)^-1/2are :

(A) [L^1/2L^-1/2]

(b) [L^-1T]

(c) [LT^-1]

(d) [L^-1/2L^1/2]

18. Speed of electromagnetic wave in free space is : (JAC, 2017)

(A) μ₀ε₀

(b) √μ₀ε₀

(c) 1/√μ₀ε₀

(d) 1/μ₀ε₀