CBSE Class 12 · 2005 · All India · Modern PhysicsVery Short Answer

Ultraviolet light is incident on two photosensitive materials having work functions

W_{1}

and

W_{2}

(W_{1} > W_{2})

. In which case will the kinetic energy of the emitted electrons be greater? Why?

Answer: Material of work function $W_{2}$ (smaller $W$ ).

Solution

From Einstein's photoelectric equation the maximum kinetic energy is

K_{ma x} = h ν - W .

For the same incident frequency

ν

, a smaller work function leaves more energy as kinetic energy.
As

W_{2} < W_{1}

, the material of work function

W_{2}

emits the more energetic electrons.

Greater KE for the material of work function W_{2}

CBSE Class 12 Board · 2005 · All India · Subjective