Electromagnetic Waves MCQs for NEET — Physics Questions with Answers

Gamma rays (γ rays) have the highest frequency among the electromagnetic waves listed. The electromagnetic spectrum is ordered by increasing frequency as follows: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays. Hence, γ rays have the highest frequency.

The maximum value of the magnetic field (B) in an electromagnetic wave can be calculated using the relation between the electric field (E) and the magnetic field (B) given by the speed of light (c): E = cB. Given that the speed of light, c = 3.0 × 10^8 m/s and E = 6.0 × 10^-4 V/m, we can solve for B:

B = E / c = (6.0 × 10^-4 V/m) / (3.0 × 10^8 m/s) = 2.0 × 10^-12 T.

Intensity of radiation is the power per unit area. The dimensional formula for power is $[M^1 L^2 T^{-3}]$ and for area is $[L^2]$. Therefore, the dimensional formula for intensity is obtained by dividing the dimensional formula of power by that of area, which gives $[M^1 L^0 T^{-3}]$.

The frequency of an electromagnetic wave does not change when it passes from one medium to another. It remains the same. Therefore, the frequency remains 3 MHz even when the wave passes through a medium with relative permeability $\varepsilon_r = 4.0$.

The frequency of an electromagnetic wave is related to its wavelength and the speed of light by the formula $\nu = \frac{c}{\lambda}$, where $\nu$ is the frequency, $c$ is the speed of light ($3 \times 10^8$ m/s), and $\lambda$ is the wavelength. For a wavelength of 25 mm (or $25 \times 10^{-3}$ m), the frequency is $\nu = \frac{3 \times 10^8}{25 \times 10^{-3}} = 1.2 \times 10^{10}$ Hz.

The energy density of an electromagnetic wave is given by the formula \( u = \frac{1}{2} (\epsilon_0 E^2 + \frac{B^2}{\mu_0}) \). The unit of energy density is Joules per cubic meter (\( Jm^{-3} \)). This is because energy density is the amount of energy stored in a given system or region of space per unit volume.

The speed of light in a vacuum is constant and does not depend on the wavelength. Hence, the ratio of the velocities of light rays of any two wavelengths in a vacuum is always 1:1.

The human eye is sensitive to light in the wavelength range of approximately 400 nm (violet) to 700 nm (red). This range is known as the visible spectrum.