CBSE Class 12 · 2004 · Modern PhysicsVery Short Answer

Two metals A and B have work functions 4 eV and 10 eV respectively. Which metal has higher threshold wavelength?

Answer: Metal A (smaller work function $\Rightarrow$ larger $λ_{0}$ ).

Solution

The threshold wavelength is

λ_{0} = \frac{h c}{W}

, so

λ_{0} \propto \frac{1}{W}

.
A smaller work function therefore means a larger threshold wavelength.
Since

W_{A} = 4 eV < W_{B} = 10 eV

, metal A has the higher threshold wavelength.

Metal A

CBSE Class 12 Board · 2004 · Subjective