Question

When a certain metallic surface is illuminated with monochromatic light of wavelength $\lambda$, the stopping potential for photoelectric current is 3$v_0$. When the same surface is illuminated with light of wavelength 2$\lambda$ , the stopping potential is $v_0$. The threshold wavelength for this surface for photoelectric effect is

• A. 6$\lambda$
• B. 4$\lambda$
• C. $\lambda$/4
• D. 8$\lambda$

Answer 1

Answer: (B)

4$\lambda$

Let the threshold wavelength of the metal he $\lambda$,
from condition-------1,

$\frac{hc}{\lambda }-\frac{hc}{{\lambda }_1}=3V_0------1$

from condition -----2,

$\frac{hc}{2\lambda }-\frac{hc}{{\lambda }_1}=V_0------2$

from 1 and 2,

${\lambda }_1=4\lambda$

So, the answer is option (B).