A monochromatic light source of intensity 5 ,mW emits 8 10^ 15 Ph… - Vidyadip

MCQ

A monochromatic light source of intensity $5\,mW$ emits $8 \times 10^{15}$ Photons per second. this light ejects photoelectrons from a metal surface. The stopping potential for this setup is $2.0\,V$ . The work function of the metal will be ............ $eV$

A
$3.9$
B
$7.9$
✓
$1.9$
D
$5.9$

✓

Answer

Correct option: C.

$1.9$

c
$P=\frac{n E}{t}$

$E = \frac{{Pt}}{n}$

$\mathrm{E}=\frac{5 \times 10^{-3}}{8 \times 10^{15}} \mathrm{\,J}$

$\mathrm{E}=\frac{5 \times 10^{-3}}{8 \times 10^{15}} \times \frac{1}{1.6 \times 10^{-19}} \mathrm{\,eV}$

$\mathrm{E}=3.9 \mathrm{\,eV}$

$(\mathrm{K.E})_{\max }=\mathrm{E}-\phi$

$\phi=3.9-2$

$\boxed{\phi = 1.9{\mkern 1mu} {\text{eV}}}$

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