NEET Properties of EM Waves MCQs & PYQs

In the electromagnetic spectrum, cosmic rays (though mostly particles, secondary cosmic rays have EM components with extremely high energy) or high-energy gamma rays have the shortest wavelengths. Among the choices, cosmic rays have the minimum wavelength.

Frequency is inversely proportional to wavelength. The order of increasing wavelength is $\gamma$ -rays, X-rays, UV-rays. Thus, the order of decreasing frequency is $\gamma$ -rays > X-rays > UV-rays, which corresponds to $b > a > c$ .

Among the given electromagnetic radiations, $\gamma$ -rays have the highest frequency and therefore the smallest wavelength, following the relation $c = \nu \lambda$ .

X-rays have wavelengths on the order of atomic spacings in solids. They are diffracted by the crystal lattice, making them suitable for investigating the structure of solids (X-ray crystallography).

In the electromagnetic spectrum, radio waves possess the lowest frequency and therefore the longest wavelength among all the given options.

The velocity of light in a medium is given by $v = \frac{1}{\sqrt{\mu \epsilon}} = \frac{1}{\sqrt{\mu_0 \mu_r \epsilon_0 \epsilon_r}}$ . Since the speed of light in vacuum is $c = \frac{1}{\sqrt{\mu_0 \epsilon_0}}$ , we get $v = \frac{c}{\sqrt{\epsilon_r \mu_r}}$ .

Conduction current is $I_c = C \frac{dV}{dt} = 20 \times 10^{-6} \times 3 = 60 \mu A$ . By Maxwell's continuity of current, the displacement current $I_d$ between the capacitor plates is equal to the conduction current in the wires, so $I_d = 60 \mu A$ .

Electromagnetic signals emitted by an antenna can propagate to another point on the Earth's surface as ground waves (traveling along the surface) or sky waves (reflected by the ionosphere). Thus, both forms are possible.

Microwave ovens heat food efficiently when the frequency of the microwaves matches the resonant frequency of water molecules, transferring energy via resonance.