Modern Physics Ques 78
- Photoelectric effect experiments are performed using three different metal plates $p, q$ and $r$ having work functions $\phi _p=2.0 $ $eV, \phi _q=2.5 $ $eV$ and $\phi _r=3.0 $ $eV$, respectively. A light beam containing wavelengths of $550 $ $nm, 450$ $ nm$ and $ 350$ $nm$ with equal intensities illuminates each of the plates. The correct $I-V$ graph for the experiment is
(2009)
(a)
(b)
(c)
(d)
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Answer:
Correct Answer: 78.(a)
Solution:
Formula:
- $E _1=\frac{1240}{550}=2.25 $ $eV, \quad E _2=\frac{1240}{450}=2.75 $ $eV$
$E _3=\frac{1240}{350}=3.54 $ $eV$
$E _1$ cannot emit photoelectrons from $q$ and $r$ plates. $E _2$ can not emit photoelectrons from $r$.
Further, work function of $p$ is least and it can emit photoelectrons from all three wavelengths. Hence magnitude of its stopping potential and saturation current both will be maximum.
BETA
