Question

light of certain wavelength strikes a metal surface with intensity x and the metal emits y electrons per second of average energy,z. what will happen to y and z if x is doubled

Answer 1

This is known as the "Photoelectric Effect" and is described by the following equation

E

max

=hν

−

 WF

M

EXmax=hνX− WFXM

where

E

max

EXmax

is the maximum kinetic energy of the electron escaping from the metal surface,

ν

ν

is the frequency of the incoming photon and

WF

M

WFXM

is the workfunction for the particular metal. Your guess is part right, doubling the intensity of the incoming beam doubles the number of electrons ejected from the metal surface, but their kinetic energy distribution remains unchanged. The maximum kinetic energy of an emitted electron is still determined by the above equation and therefor still capped by

E

max

EXmax

and the kinetic energies of all electrons emitted are still distributed from 0 to

E

max

EXmax

Answer 2

Given:

Intensity of light $=X$

Electrons emitted per second$=Y$

Average energy $=Z$

To Find: $Y$ and $Z$ if $X$ is doubled

Solution:

Suppose that the wavelength of light is $\[\lambda \]$.

The number of emitted electrons depends upon the intensity of light. It varies directly with the intensity of light, i.e.,

Number of emitted electrons $\[ \propto \]$ Intensity of light

Therefore, if $X$ is doubled, then the number of emitted electrons per second, i.e., $Y$ will also be doubled.

However, there will be no change in the average energy of light.

Hence, if $X$ is doubled, $Y$ is doubled and $Z$ remains the same.

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