Question

In an electromagnetic wave, the electric and magnetic fields are $100V{m^{ - 1}}$ and $0.265A{m^{ - 1}}$. The maximum energy flow is
(A) $26.5W{m^{ - 2}}$
(B) $36.5W{m^{ - 2}}$
(C) $46.7W{m^{ - 2}}$
(D) $765W{m^{ - 2}}$

Answer 1

Hint: We know that the electromagnetic waves consist of an electric field and magnetic field oscillating perpendicular to each other and together they propagate in space with the speed of light and hence they carry energy so here we will find the net maximum flow of energy with the given data.

Formula Used:
If E is the magnitude of electric field and H is the magnitude of magnetic field then a term is used to indicate the energy flow called Poynting vector S which is related as
$S = E \times H$

Complete answer:
According to the question, we have given that the magnitude of the electric field in an electromagnetic wave is $E = 100V{m^{ - 1}}$ and the magnitude of the magnetic field corresponding to the electric field of the same electromagnetic wave is given as $H = 0.265A{m^{ - 1}}$

The net amount of maximum energy flow is calculated using the formula:
$S = E \times H$

On substituting the values of the parameters we get,
$
  S = 0.265 \times 100 \\
  S = 26.5W{m^{ - 2}} \\
 $

So, the amount of net maximum flow of energy in the given electromagnetic wave is $S = 26.5W{m^{ - 2}}$

Hence, the correct answer is option (A) $26.5W{m^{ - 2}}$.

Note: Here S, E, and H are written in vector form and E and H have the vector product but since E and H are always perpendicular to each other so the product is simply written in their magnitude forms, S is called Poynting vector represents the direction of flow of energy and its magnitude represent the maximum amount of flow of energy.