Question

A filter transmits only the radiation of wavelength $\ge 440$ nm. Radiation from a hydrogen discharge tube goes through such a filter and is incident on a metal of work function $2.0eV$. Find the stopping potential which can stop

• A. 1.4 V
• B. 1.3 V
• C. 0.85 V
• D. 0.55 V

Answer 1

Answer: (D)

0.55 V

$H_{\beta }$ line has wavelength

$\lambda =\frac{1240}{2.55}=486.1nm$

Apply $e{V}_s=hf-\varphi$
$=2.55-2.0=0.55eV$
$V_s=0.55V$

So, the answer is option (D).