Question

If mean wavelength of light radiated by 100 W lamp is 5000 $\stackrel{\circ }{A}$, then number of photons radiated per second are

• A. $3\times {10}^{23}$
• B. $2.5\times {10}^{22}$
• C. $2.5\times {10}^{20}$
• D. $5\times {10}^{17}$

Answer 1

The correct option is C

$2.5\times {10}^{20}$

$P=\frac{nhc}{\lambda t}\Rightarrow \frac{n}{t}=\frac{P.\lambda }{hc}=\frac{100\times 5000\times {10}^{-10}}{6.6\times {10}^{-34}\times 3\times {10}^8}$
$=2.50\times {10}^{20}$