Question:

The electric field and magnetic field components of an electromagnetic wave going through vacuum are described by:
\[ E_x = E_0 \sin(kz - \omega t), \quad B_y = B_0 \sin(kz - \omega t). \]
Then the correct relation between \( E_0 \) and \( B_0 \) is given by:

Updated On: Mar 19, 2025
  • \(E_0 B_0=\omega k\)

  • \(E _0= kB _{ 0}\)

  • \(kE _{ 0 }=\omega B _{ 0 }\)

  • \(\omega E _{ 0 }= kB _{ 0 }\)

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The Correct Option is C

Approach Solution - 1

For an electromagnetic wave propagating in vacuum:

  • The speed of the wave \( c \) is related to the angular frequency \( \omega \) and the wave number \( k \): \[ c = \frac{\omega}{k}. \]
  • The speed of light \( c \) in terms of the electric field \( E_0 \) and magnetic field \( B_0 \) is given by: \[ c = \frac{E_0}{B_0}. \]

Equating both expressions for \( c \):

\[ \frac{\omega}{k} = \frac{E_0}{B_0}. \]

Rearranging terms:

\[ kE_0 = \omega B_0. \]

Thus, the correct relation is:

\[ kE_0 = \omega B_0. \]

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Approach Solution -2

The correct answer is (C) : $kE _{ 0 }=\omega B _{ 0 }$
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Questions Asked in JEE Main exam

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Concepts Used:

Electromagnetic waves

The waves that are produced when an electric field comes into contact with a magnetic field are known as Electromagnetic Waves or EM waves. The constitution of an oscillating magnetic field and electric fields gives rise to electromagnetic waves.

Types of Electromagnetic Waves:

Electromagnetic waves can be grouped according to the direction of disturbance in them and according to the range of their frequency. Recall that a wave transfers energy from one point to another point in space. That means there are two things going on: the disturbance that defines a wave, and the propagation of wave. In this context the waves are grouped into the following two categories:

  • Longitudinal waves: A wave is called a longitudinal wave when the disturbances in the wave are parallel to the direction of propagation of the wave. For example, sound waves are longitudinal waves because the change of pressure occurs parallel to the direction of wave propagation.
  • Transverse waves: A wave is called a transverse wave when the disturbances in the wave are perpendicular (at right angles) to the direction of propagation of the wave.