Test: Electromagnetic waves (25 Dec) - JEE MCQ

μ₀ is called the permeability of free space and similarly, ε₀ is called the permittivity of free space.

All regions have the same speed.
The speed of a wave is not dependent upon its frequency and wavelength but rather upon the properties of the medium through which it travels.
 

A gamma ray or gamma radiation is a penetrating electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves and so imparts the highest photon energy

Maxwell predicted that an accelerated charge produces a sinusoidal time varying magnetic field, which in turn produces a sinusoidal time varying electric field. These two fields are mutually perpendicular to each other and sources of each other. They (fields) form an electromagnetic wave i.e. the wave that is propagated by simultaneous periodic variations of electric field and magnetic field intensity.

In electromagnetic waves the ratio of amplitudes of electric field and magnetic field is equal to the velocity of the electromagnetic waves in free space.

(E₀ / B₀) = c

Properties:
• Electromagnetic waves are propagated by oscillating electric and magnetic fields oscillating at right angles to each other. Hence (a) is incorrect.
• Electromagnetic waves travel with a constant velocity of  3 x 108 ms^-1 in vacuum. Hence (c) is incorrect.
• Electromagnetic waves need no medium of propagation. The energy from the sun is received by the earth through electromagnetic waves. Hence, correct answer is (b).

Electromagnetic waves are not used to determine global warming.

Red light has the lowest energy and is least scattered and has thus least frequency, thus we get that it has the largest wavelength. Similarly violet has maximum frequency.

V(velocity/speed)= ω/wave number (K)
V= 12×10¹⁵/4×10⁷
V=3×10⁸ m/s

X-ray wavelength is in range of 10−11m to 10−8m

So option C is correct.