Question

A laser beam transfers an energy of $5\text{J}$ across an area of $1\times {10}^{-2}{\text{m}}^2$ in a time of ${10}^{-9}\text{s}$. What is the intensity of the beam?

Answer 1

Given:

Energy $=5\text{J}$

Area$=1\times {10}^{-2}{\text{m}}^2$

Time $={10}^{-9}\text{s}$


Intensity $\left(I\right)=\text{Power}/\text{Area}=\text{Energy}/(\text{Area}\times \text{Time})$

Intensity$\left(I\right)=\frac{5}{1\times {10}^{-2}\times {10}^{-9}}=5\times {10}^{11}{\text{watt/m}}^2$

Hence, Option $\left(C\right)$ is the correct answer.