Light of wavelength 5000 , , A ^o falling on a sensitive surface.…

MCQ

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

A
$5\times 10^{11}$
✓
$2.5\times 10^{11}$
C
$3\times 10^{11}$
D
none of these

✓

Answer

Correct option: B.

$2.5\times 10^{11}$

b
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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