Question

What is photoelectric effect?
Define
(i) Stopping potential,
(ii) Photoelectric work function.

Answer 1

In case of photoelectric effect, the cathode is hit by a beam of photons which causes electrons in cathode to come out of the cathode and go to anode. Potential difference is maintained between cathode and anode. The intensity of the incident light determines the current and the energy of the incident light determines the maximum energy of the electron.

Formula used:
$E = \dfrac{{hc}}{\lambda } - \phi$

Complete answer:
When radiation is hit on the cathode some of the energy of that radiation will be used by the electron to come out of that electrode which is called a work function and the remaining energy is used as a kinetic energy to reach the anode. When an electron reaches anode automatically current is generated. The amount of current produced depends on the intensity of the radiation.
We can assume that each photon will bring one electron out of the metal. Hence ‘n’ photons will bring ‘n’ electrons out of the metal. The power of the radiation is given by
$W = \dfrac{{nhc}}{{\lambda t}}$
Energy of each photon is given by $\dfrac{{hc}}{\lambda }$ and $\phi$ is work function and $E$ is the remaining energy which is used as kinetic energy.
They are related as $E = \dfrac{{hc}}{\lambda } - \phi$.
Now that kinetic energy can be related to stopping potential.
$E = eV$
Here ‘V’ is the stopping potential. ‘e’ is the charge of an electron.
If we apply stopping potential at anode then the electron that came out of the cathode can never reach anode.

Note:
It doesn’t matter if we increase the number of photons, but as long as the photon energy is less than the required work function, the electron will not emit from the metal. If we apply the stopping potential at the anode then no electron will reach the anode and there will be no photoelectric current.