Electromagnetic Waves MCQs for NEET — Physics Questions with Answers

In a plane electromagnetic wave, the electric field and magnetic field oscillate sinusoidally with time. The average value of a sinusoidal function over a complete cycle is zero. Therefore, the average value of the electric field ( extbf{E}) in a plane electromagnetic wave is zero.

The refractive index \( n \) of a medium is given by the square root of the product of its relative permeability \( \mu_r \) and dielectric constant \( \kappa \). Mathematically, \( n = \sqrt{\mu_r \kappa} \). Hence, the correct option is \( \sqrt{\mu_r \kappa} \).

To find the frequency \( f \) of the radiation, we use the relation \( c = \lambda f \), where \( c \) is the speed of light, \( \lambda \) is the wavelength, and \( f \) is the frequency. Given \( \lambda = 21 \text{ cm} = 0.21 \text{ m} \) and \( c = 3 \times 10^8 \text{ m/s} \), we can calculate the frequency as: \[ f = \frac{c}{\lambda} = \frac{3 \times 10^8}{0.21} = 1.428 \times 10^9 \text{ Hz} = 1.428 \text{ GHz} \] Hence, the correct option is 1.428 GHz.

The relationship between the electric field (E) and the magnetic field (B) in an electromagnetic wave is given by:

$$ B = rac{E}{c} $$

Given, E = $900 ext{ NC}^{-1}$ and c = $3 imes 10^8 ext{ m/s}$, we can calculate the magnetic field (B) as:

$$ B = rac{900}{3 imes 10^8} = 3 imes 10^{-6} ext{ T} $$

Hence, the correct option is $3 imes 10^{-6} ext{ T}$.

Electromagnetic waves are produced by an accelerating charge. When a charge accelerates, it creates a changing electric field, which in turn creates a changing magnetic field, leading to the production of electromagnetic waves. This is a fundamental concept in electromagnetism.

Maxwell's equations are derived from the laws of both electricity and magnetism. These four equations describe how electric fields and magnetic fields interact and propagate. They are crucial for understanding classical electromagnetism.

Radio waves have the longest wavelength among the given options. The electromagnetic spectrum is ordered by wavelength, with radio waves having the longest wavelengths, followed by infrared, visible light, and then X-rays with the shortest wavelengths.