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In the photoelectric experiment, if we u...

In the photoelectric experiment, if we use a monochromatic light, the` I – V` curve is as shown. If work function of the metal is 2 eV, estimate the power of light used. (Assume efficiency of photo emission `=10^(-3)`, i.e. number of photoelectrons emitted are `10^(-3)` times of number of photons incident on metal).

A

(a)2 W

B

(b)5 W

C

(c)7 W

D

(d)10 W

Text Solution

Verified by Experts

The correct Answer is:
C
The energy of incident photons is given by `hv=eV_(s)+phi_(0)=2+5=7eV`
(`V_(s)` is stopping potential and `phi_(0)` is work function)
`10^(-3)n_(ph)=n_(e)" "rArr" "n_(ph)=10^(3)n_(e)" "rArr" "l_(s)=n_(s)e`
`rArr" "P=n_(ph)hv" "rArr" "P=10^(3)xxn_(e)xx7eV`
`rArr" "P=10^(3)xx(l_(s))/(e)xx7eV" "rArr" "(10^(3)xx10^(-5))/(e)(7eV)=P,P=7xx10^(-2)W`
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