During the propagation of electromagnetic waves in a medium:

• Electric energy density is equal to the magnetic energy density.

• Both electric and magnetic energy densities are zero.

• Electric energy density is double of the magnetic energy density.

• Electric energy density is double of the magnetic energy density.

An electromagnetic wave in vaccum has the electric and magnetic fields  and which are always perpendicular to each other. the direction of polarisation is given by  and that of wave propagation by  then

3.

The threshold frequency for a metallic surface corresponds to an energy of 6.2 eV, and the stopping potential for a radiation incident on this surface 5 V. The incident radiation lies in

• X-ray region

• ultra-violet region

• infra-red region

• infra-red region

The direction of propagation of electromagnetic wave is along

• Electric field vector, E

• Magnetic field vector, B

• E . B

• E × B

Assume that a radio station is about 200 km away at your location and the station operates 972 kHz. How long does it take for an electromagnetic signal to travel from the station to you and how many wave crests does it send out per second ?

• 666 µs and 9.72 × 10⁵ crests per second

• 666 µs and 972 × 10⁵ crests per second

• 555 µs and 97.2 × 10⁷ crests per second

• 555 µs and 0.972 × 10⁵ crests per second

The electric field portion of an electromagnetic wave is given by (all variables in SI units) E = 10^-4 sin(6 x 10⁵ t − 0.01 x). The frequency (f) and the speed (v) of electromagnetic wave are

• f = 30/π kHz and v = 1.5 × 10⁷ m/s

• f = 90/π kHz and v = 6.0 × 10⁷ m/s

• f = 300/π kHz and v = 6.0 × 10⁷ m/s

• f = 600/π kHz and v = 7.5 × 10⁷ m/s

γ-rays are detected by

• point contact diodes

• thermopiles

• ionization chamber

• photocells

If the directions of electric and magnetic field vectors of a plane electromagnetic wave are along positive y- direction and positive z-direction respectively, then the direction of propagation of the wave is along

• positive z-direction

• negative z-direction

• negative y-direction

• positive x-direction

The amplitudes E₀ and B₀ of electric and the magnetic component of an electromagnetic wave respectively are related to the velocity c in vacuum as

• ${\mathrm{E}}_0{\mathrm{B}}_0 = \frac{1}{\mathrm{c}}$

• ${\mathrm{E}}_0 = \frac{\mathrm{c}}{{\mathrm{B}}_0}$

• B₀ = cE₀

• E₀ = cB₀

Identify the mismatched pair.

• Microwaves  —  Aircraft navigation

• Radio waves  —  Cellular phone

• γ rays   —  Klystron

• Ultraviolet rays   —  LASIK