A monochromatic beam of frequency and power falls normally on a clean metallic…

PHYSICS · Multi-part · A Level · Physics · Particles and radiation · Particles and radiation

Problem

A monochromatic beam of frequency

\nu\,(>\nu_0)

and power

P

falls normally on a clean metallic surface of area

A

. A fraction

r

of the incident power is reflected, and the quantum efficiency of photoemission (ratio of emitted electrons to absorbed photons) is

\eta

. Assume that every emitted electron is collected by the anode when a sufficiently large positive potential is applied. (i) Derive an expression for the saturation photocurrent

I_{\text{sat}}

in terms of

P,\;r,\;\eta,\;h,\;\nu

and the electronic charge

e

. (ii) Using your expression, calculate

I_{\text{sat}}

for

P=2.0\,\text{mW}

\nu=6.0\times10^{14}\,\text{Hz}

r=0.25

and

\eta=0.05

. (iii) Keeping

P

fixed, discuss qualitatively how

I_{\text{sat}}

will change if the frequency of the incident light is increased while still remaining above the threshold frequency.

Related theory

Browse the problem library