Physics MCQs for NEET — Practice Questions with Answers

When a plane electromagnetic wave is incident on a material surface, it delivers both momentum and energy. The energy carried by the wave is related to the intensity of the wave, and the momentum is related to the energy by the equation $P = rac{E}{c}$, where $c$ is the speed of light. Therefore, both momentum and energy are non-zero. Hence, the correct option is $P eq 0, E eq 0$.

The velocity of electromagnetic waves in a vacuum is the speed of light, which is approximately $3 imes 10^8$ meters per second. This speed is the same for all types of electromagnetic waves, including gamma rays ($V_ ext{γ}$), X-rays ($V_ ext{x}$), and microwaves ($V_ ext{m}$). Therefore, $V_ ext{γ} = V_ ext{x} = V_ ext{m}$.

According to Maxwell's equations, a changing electric field produces a magnetic field. This relationship is described by the Maxwell-Ampère law: $$ abla imes extbf{E} = -rac{ ext{d} extbf{B}}{ ext{d}t}$$ which indicates that a time-varying electric field generates a magnetic field.

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.