Question

A certain source of radiation emits $8\times {10}^{15}{\text{quanta sec}}^{-1}$. Calculate the power output in ${\text{J sec}}^{-1}$.
Given: $\lambda =840\text{nm}$

• A. $2.55\times {10}^{-3}{\text{J sec}}^{-1}$
• B. $1.89\times {10}^{-3}{\text{J sec}}^{-1}$
• C. $3.28\times {10}^{-3}{\text{J sec}}^{-1}$
• D. $1.32\times {10}^{-3}{\text{J sec}}^{-1}$

Answer 1

The correct option is B $1.89\times {10}^{-3}{\text{J sec}}^{-1}$

We know,
$E=nhv=n\times \frac{hc}{\lambda }$
$\text{Power output}=\text{No. of quanta}\times \frac{hc}{\lambda }$
$=\frac{8\times {10}^{15}\times 6.62\times {10}^{-34}\times 3\times {10}^8}{840\times {10}^{-9}}$
$=1.89\times {10}^{-3}{\text{J sec}}^{-1}$