Advertisement Remove all ads

# The Energy Contained in a Small Volume Through Which an Electromagnetic Wave is Passing Oscillates with - Physics

MCQ

The energy contained in a small volume through which an electromagnetic wave is passing oscillates with

#### Options

• zero frequency

•  the frequency of the wave

• half the frequency of the wave

• double the frequency of the wave

Advertisement Remove all ads

#### Solution

double the frequency of the wave

The energy per unit volume of an electromagnetic wave,

u = 1/2 ∈_0 E^2 + B^2/(2u_0)

The energy of the given volume can be calculated by multiplying the volume with the above expression.

U = u xx V = (1/2 ∈_0 E^2 + B^2/(2u_0)) xx V ...(1)

Let the direction of propagation of the electromagnetic wave be along the z-axis. Then, the electric and magnetic fields at a particular point are given by
Ex= E0 sin (kz – ωt)
By= B0 sin (kz – ωt)

Substituting the values of electric and magnetic fields in (1), we get :

U = (1/2 ∈_0 (E_0^2 sin^2(kz - ωt) + (B_0^2sin^2(kz – ωt))/(2u_0)) xx V

⇒ U = (∈_0 E_0^2 ((1-cos(2kz - 2ωt)))/4 + (B_0^2(1-cos(2kz-2ωt)))/(4u_0)) xx V

From the above expression, it can be easily understood that the energy of the electric and magnetic fields have angular frequency 2ω. Thus, the frequency of the energy of the electromagnetic wave will also be double.

Is there an error in this question or solution?
Advertisement Remove all ads

#### APPEARS IN

HC Verma Class 11, Class 12 Concepts of Physics Vol. 2
Chapter 18 Electromagnetic Waves
MCQ | Q 5 | Page 339
Advertisement Remove all ads

#### Video TutorialsVIEW ALL 

Advertisement Remove all ads
Share
Notifications

View all notifications

Forgot password?