and
shinning on a metal surface kept at a distance 2 m. Assume that the metal surface
has work function of 2
and
that each atom on the metal surface can be treated as a circular disk of radius
1.5.
(i) Estimate no. of photons emitted by the bulb per
second. [Assume no other losses] (ii) Will there be photoelectric emission?
(ii'i) How much time would be required by the atomic disk to receive energy
equal to work function ()? (iv)How
many photons would atomic disk receive within time duration calculated in (iii)
above? (v) Can you explain how photoelectric effect was observed
instantaneously? [Hint: Time calculated in part (iii) is from classical
consideration and you may further take the target of surface area say 1 cm2
and estimate what would happen ?]
Answer:
(i) No. of
photon emitted by bulb per second is
(ii) Energy of the incident photon 
As this energy is greater than 2eV (i.e.,
work function of metal surface ), hence photoelectric emission takes place.
(iii) Let 
t
be the time spent in getting the energy 
(=work
function of metal.) Refer Fig 7(EP) .5,
(iv) No. of emission of
electrons is 11.04 s, hence the photoelectric emission is not instantaneous in
this problem.
(v)
In photoelectric emission, there is an elastic collision between incident
photon and free electron of the metal surface, which lasts for very very short
interval of time 
, hence we say
photoelectric emission is instantaneous.
You need to login to perform this action.
You will be redirected in
3 sec
