Which one of the following statements is wrong ?

• Radio waves in the frequency range 30 MHz to 60 MHz are called sky waves.

• Radio horizon of the transmitting antenna for space wave is ${\mathrm{d}}_{\mathrm{T}} = \sqrt{\left(2{\mathrm{Rh}}_{\mathrm{T}}\right)}$ (R = radius of earth, h_T = height of transmitting antenna)

• Within the skip distance neither the ground waves nor the sky waves are received

• The principle of fibre optical communication is total internal reflection

A plane electromagnetic wave travels in free space along x-axis. At a particular point in space, the electric field along y-axis is 9.3 Vm^-1. The magnetic induction is

• 3.1 × 10^-8 T

• 3 × 10^-5 T

• 3 × 10^-6 T

• 9.3 × 10^-6 T

The dielectric constant of air is 1.006. The speed of electromagnetic wave travelling in air is a x 10⁸ ms^-1, where a is about

• 3

• 3.88

• 2.5

• 3.2

1. The wavelength of microwaves is greater than that of UV-rays.
2. The wavelength of IR rays is lesser than that of UV-rays.
3. The wavelength of microwaves is lesser than that of IR rays.
4. Gamma rays have shortest wavelength in the electromagnetic spectrum.

Of the above statements

• A and B are true

• B and C are true

• A and D are true

• A and C are true

The frequency of X-rays, γ-rays and ultraviolet rays are respectively a, b and c then

• a < b, b > c

• a > b, b > c

• a > b, b < c

• a < b, b < c

The waves relevant to telecommunications are

• visibe light

• infrared

• ultraviolet

• microwave

Velocity of electromagnetic waves in a medium depends upon

• thermal properties of medium

• mechanical and electrical properties of medium

• electrical and magnetic properties of the medium

• mechanical and magnetic properties of the medium

In the electromagnetic spectrum, the visible spectrum lies between

• radiowaves and microwaves

• infrared and ultraviolet rays

• microwaves and infrared spectrum

• X-ray and γ-ray spectrum

Maxwell in his famous equation of electromagnetism introduced the concept

• AC current

• DC current

• displacement current

• impedance

30.

Out of the following electromagnetic radiations, which has the shortest wavelength ?

• Radiowaves

• Infrared

• X-rays

• Visible light