Question

Threshold wavelength for photoelectric emission from a metal surface is $5200\mathring{A}$ . Photoelectrons will be emitted when this surface is illuminated with monochromatic radiation from:

• A. $1W$ IR lamp
• B. $50W$ UV lamp
• C. $50W$ IR lamp
• D. $10W$ IR lamp

Answer 1

The correct option is B $50W$ UV lamp

Photoelectrons will be emitted when the energy of incident light is greater than the threshold energy. Hence,

$\frac{hc}{\lambda }>\frac{hc}{{\lambda }_{th}}$

Hence, $\lambda <{\lambda }_{th}$

Thus, $\lambda <5200$. This condition is satisfied by UV rays since ${\lambda }_{UV}<3800A$.