Question

The frequency and intensity of a light source are both doubled. Consider the following statements.

A. The saturation photocurrent remains almost the same

B. The maximum kinetic energy of the photoelectrons is doubled

• A. Both A and B are true
• B. A is true but B is false
• C. A is false but B is true
• D. Both A and B are false

Answer 1

The correct option is B

A is true but B is false

This is what we know from the question:

1. The frequency has been doubled from to v to 2v.

2. The intensity has also been doubled. Since intensity I is given by –

$I=\frac{energy}{unittime.unitarea}=\frac{\Delta \left(nhv\right)}{\Delta t.\Delta A},$

doubling v naturally doubles the intensity as well, keeping the number of photons hitting the emitter plate a constant.

We know that the saturation photocurrent stays roughly the same if the number of photons hitting the plate is kept constant.

Also, the photoelectric equation tells us, that the maximum kinetic energy of the photoelectrons will be related to the frequency of light, ν, as -

$K.E_{max}=hv-W\Rightarrow V=\frac{k.E_{max}+W}{h}$

Clearly, doubling ν will not double the $K.E_{max}$

Hence, (b) is the correct choice!