Question

The work functions for sodium and copper are 2eV and 4eV. Which of them is suitable for a photocell with $4000\stackrel{\circ }{A}$ light

• A. Copper
• B. Sodium
• C. Both
• D. Neither of them

Answer 1

The correct option is B

Sodium

Threshold wavelength for Na, ${\lambda }_{Na}=\frac{12375}{2}=6187.5\stackrel{\circ }{A}$
$Also{\lambda }_{Cu}=\frac{12375}{4}=3093.75$
$Since{\lambda }_{Na}>4000\stackrel{\circ }{A};$ So Na is suitable.