Question

The sun delivers 10³ W m^-2 of electromagnetic flux on the earth's surface. The total power that is incident on a roof of dimensions 6m × 30m is
$\eqalign{
  & {\text{A) 1}}{\text{.8 }} \times {\text{ 1}}{{\text{0}}^5}{\text{ W}} \cr
  & {\text{B) 7}}{\text{.2 }} \times {\text{ 1}}{{\text{0}}^5}{\text{ W}} \cr
  & {\text{C) 0}}{\text{.9 }} \times {\text{ 1}}{{\text{0}}^5}{\text{ W}} \cr
  & {\text{D) 4}}{\text{.5 }} \times {\text{ 1}}{{\text{0}}^5}{\text{ W}} \cr} $

Answer 1

Hint:Total power of incident can be considered as the strength, The strength is defined as the force per unit area and the force is defined as the energy per unit time.

Complete step by step solution:
Given Electromagnetic flux = 10³ W m^-2
$\eqalign{
  & {\text{The area of roof A = 6m }} \times {\text{ 30m}} \cr
  & {\text{The area of roof A}} = {\text{ 180 }}{{\text{m}}^2} \cr
  & {\text{The strength is defined as the force per unit area and the force is defined as the energy per unit time}} \cr
  & \Rightarrow {\text{P = 1}}{{\text{0}}^3}{\text{ }} \times {\text{ 180}} \cr
  & \therefore {\text{ P = 1}}{\text{.8 }} \times {\text{ 1}}{{\text{0}}^5}{\text{ W}} \cr} $

Hence option A is correct

Additional Information: Electromagnetic waves can bring energy to a system based on their electric and magnetic fields. These fields can increase forces and transfer charge in the system and thus, work on them. If the frequency of the electromagnetic wave is similar to the system's natural frequencies (such as microwaves at the resonant frequency of water molecules), the transfer of energy is more efficient.
But an electromagnetic wave carries energy, whether it is absorbed or not. Once created, farms move energy away from a source. If absorbed, the field strength decreases and nothing is left on the trip. Clearly, the greater the strength of the electric and magnetic fields, the more they can work and the more energy the electromagnetic wave will provide. The energy of a wave is proportional to its amplitude squared (E² or B²). This applies to waves on guitar strings, for water waves and sound waves, where the amplitude is proportional to the pressure. In electromagnetic waves, amplitude is the maximum field strength of the electric and magnetic fields.

Note: Analysis of the propagation of electromagnetic waves through a stratified medium or with transmission systems such as wave guides and coupled conductors is often expressed in terms of incident, reflected and transmitted power components.