Question
Light of wavelength $5000\,\,\mathop A\limits^o $ falling on a sensitive surface. If the surface has received $10^{-7}\,J$ of energy, then the number of photons falling on the surface will be
✓
Answer
Energy of one photon $=\frac{\mathrm{hc}}{\lambda}=4 \times 10^{-19}=\mathrm{E}$
$(n)$ $(\mathrm{E})=$ Energy $=10^{-7}$
$(n)$ $\left(4 \times 10^{-19}\right)=10^{-7}$
$\mathrm{n}=2.5 \times 10^{11}$
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