Question

A certain laser transition emits $6.37\times {10}^{15}$ quanta per second per square metre. Calculate the power output in joule per square metre per second( Given $\lambda =632.8nm$):

• A. $3.14\times {10}^{-19}J{m}^{-2}$ $se{c}^{-1}$
• B. $4\times {10}^{-3}J{m}^{-2}$ $se{c}^{-1}$
• C. $2\times {10}^{-3}J{m}^{-2}$ $se{c}^{-1}$
• D. $4.03\times {10}^{9}J{m}^{-2}$ $se{c}^{-1}$

Answer 1

The correct option is C $2\times {10}^{-3}J{m}^{-2}$ $se{c}^{-1}$

Energy falling per square meter per second=No.of quanta falling per square meter per second\times Energy of one quanta

$=6.37\times {10}^{15}\times hc/\lambda$

$=\frac{6.37\times {10}^{15}\times 6.626\times {10}^{-34}\times {10}^8}{632.8\times {10}^{-9}}$

$=2\times {10}^{-3}J{m}^{-2}$ $se{c}^{-1}$