Light of uniform intensity impinges perpendicularly on a totally reflecting surface. If the area of the surface is halved, the radiation force on it will become

CONCEPT:

Intensity (I):

• The energy crossing per unit area per unit time, perpendicular to the direction of propagation of EM wave is called intensity.
• Mathematically it is written as,

\(\Rightarrow I =\frac{Total\, EM\, energy}{Surface \,area \times Time}=\frac{Total\, energy\, density \,\times\, Volume}{Surface \, area \times Time}\)

EXPLANATION:

• From the above equation, it is clear that the intensity of the EM wave is inversely proportional to the surface area i.e., 

\(\Rightarrow Intensity \propto\frac{1}{Surface \, area}\)

• Hence, if the area of the surface is halved, the radiation force on it will become double. Therefore option 1 is correct.