Question

Which metal will be suitable for a photoelectric cell using light of wavelength $4000\mathring{A}$ The work functions of sodium and copper are respectively 2eV and 4eV

• A. Sodium
• B. Copper
• C. Both
• D. None of these

Answer 1

The correct option is A Sodium

Energy of incident radiation is given by:

$E=\frac{hc}{\lambda }=\frac{3\ast {10}^8\ast 6.64\ast {10}^{-34}}{4000\ast {10}^{-10}}=4.98\ast {10}^{-19}=3.1125eV$

Hence it can be used to excite any metal surface whose work function is less than $3.1125eV.$