Modern Physics 2 Question 17
16. Photoelectric effect experiments are performed using three different metal plates $p, q$ and $r$ having work functions $\varphi _p=2.0 eV, \varphi _q=2.5 eV$ and $\varphi _r=3.0 eV$, respectively. A light beam containing wavelengths of $550 nm, 450 nm$ and $\quad 350$ $nm$ with equal intensities illuminates each of the plates. The correct $I-V$ graph for the experiment is
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Solution:
- $E _1=\frac{1240}{550}=2.25 eV, \quad E _2=\frac{1240}{450}=2.75 eV$
$E _3=\frac{1240}{350}=3.54 eV$
$E _1$ 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.
