Question

The photoelectric currents at distances $r_1$ and $r_2$ of light source from photoelectric cell are $I_1$ and $I_2$ respectively. The value of ($\frac{I_1}{I_2}$) will be

• A. $\frac{r_1}{r_2}$
• B. ${\left(\frac{r_1}{r_2}\right)}^2$
• C. $\frac{r_2}{r_1}$
• D. ${\left(\frac{r_2}{r_1}\right)}^2$

Answer 1

The correct option is D ${\left(\frac{r_2}{r_1}\right)}^2$

Relation between photoelectric current and distance is as follows

$I=\frac{P}{4\pi r^2}$

$so,$

$I_1=\frac{P}{4\pi {r_1}^2}$

$I_2=\frac{P}{4\pi {r_2}^2}$

Diving I₂ by I₁

$\frac{I_2}{I_1}={\left(\frac{r_2}{r_1}\right)}^2$