Electromagnetic Waves

In a plane electromagnetic wave, the electric field of amplitude 1 Vm^-1 varies with time in free space. The average energy density of magnetic field is (in Jm^-2)

• 8.86 × 10^-12

• 4.43 × 10^-12

• 17.72 × 10^-12

• 2.21 × 10^-12

Which one of the following is the property of a monochromatic, plane electromagnetic wave in free space?

• Electric and magnetic fields have a phase difference of $\frac{\mathrm{\pi }}{2}$

• The energy contribution of both electric and magnetic fields are equal.

• The direction of propagation is in the direction of electric field E

• The pressure exerted by the wave is the product of energy density and the speed of the wave

If the magnetic field of an electromagnetic wave is given as B_y = 2 x 10^-7 sin (10³ x + 1.5x 10¹² t) tesla, the wavelength of the electromagnetic wave is

• 0.314 mm

• 0.628 mm

• 6.28 mm

• 1.26 mm

The electromagnetic waves travel with

• the same speed in all media

• the speed of sound in free space

• the speed of light c = 3 x 10⁸ ms^-1 in free space

• the speed of light c = 3 x 10⁸ ms^-1 in fluid medium

The speed of an electromagnetic wave in a material medium of permeability µ and permittivity is

• $\frac{1}{\mathrm{\mu \epsilon }}$

• $\frac{1}{2\mathrm{\mu \epsilon }}$

• $\frac{1}{\sqrt{\mathrm{\mu \epsilon }}}$

• $\frac{1}{\sqrt{2\mathrm{\mu \epsilon }}}$

The energy of infrared waves is greater than that of

• visible light

• ultraviolet waves

• micro waves

• gamma rays

Which one of the following is incorrect statement in the transmission of electromagnetic waves?

• Ground wave propagation is for high frequency transmission.

• Sky wave propagation is facilitated by ionospheric layers.

• Space wave is of high frequency and is suitable for line of sight communication.

• Space wave is used for satellite communication.

The electric field of an electromagnetic wave travelling through vacuum is given by the equation E = Eo sin(kx − ωt). The quantity that is independent of wavelength is

• $\frac{\mathrm{k}}{\mathrm{\omega }}$

• kω

• ω

• k

The electric field of a plane electromagnetic wave varies with time of amplitude 2 Vm^-1 propagating along z-axis. The average energy density of the magnetic field is (in Jm^-3)

• 13.29 × 10^-12

• 8.86 × 10^-12

• 17.72 × 10^-12

• 4.43 × 10^-12

Electromagnetic waves of frequencies higher than $9\sqrt{2}$ MHz are found to be reflected by the ionosphere on a particular day at a place. The maximum electron density in the ionosphere is

• $\sqrt{5} \times {10}^{12} {\mathrm{m}}^{-3}$

• $\sqrt{2} \times {10}^{12} {\mathrm{m}}^{-3}$

• 2 × 10¹² m^-3

• 5 × 10¹² m^-3