Question:

The pressure exerted by an electromagnetic wave of intensity $I\left( W / m ^{2}\right)$ on a non-reflecting surface is: $[c$ is the velocity of light $]$

Updated On: Apr 28, 2023
  • $Ic$
  • $Ic^2$
  • $I/c$
  • $I/c^2$
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The Correct Option is C

Solution and Explanation

Force per unit area is the radiation pressure. When a surface intercepts electromagnetic radiation, a force and a pressure are exerted on the surface. As the surface is non-reflecting, so, it is completely absorbed and in such case the force is, $F=\frac{I A}{c}$ where $I$ is intensity of light. $A$ is area of surface and $c$ is velocity of electromagnetic wave. The radiation pressure is the force per unit area i.e., $P=\frac{F}{A}=\frac{I}{C}$
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Concepts Used:

Pressure

Pressure is defined as the force applied perpendicular to the surface of an object per unit area over which that force is distributed.

Everyday examples of pressure are:

  • The working of the vacuum cleaner is an example of pressure. The fan inside the vacuum creates a low-pressure region which makes it easy to suck the dust particles inside the vacuum.
  • Using a knife for cutting is another example of pressure. The area exposed from the knife is small but the pressure is high enough to cut the vegetables and fruits.

Formula:

When a force of ‘F’ Newton is applied perpendicularly to a surface area ‘A’, then the pressure exerted on the surface by the force is equal to the ratio of F to A. The formula for pressure (P) is:

P = F / A

Units of Pressure:

The SI unit of pressure is the pascal (Pa)

A pascal can be defined as a force of one newton applied over a surface area of a one-meter square.