State two important properties of photon which are used to write Einstein's photoelectric equation. Define (i) stopping potential and (ii) threshold frequency, using Einstein's equation and drawing necessary plot between relevant quantities.

The two important properties of photon for photoelectric effect are:
a) The energy of photon is quanta or discrete.
b) The energy of photon is proportional to the frequency of light.
i) Stopping potential: This is the value of negative potential of anode at which the photoelectric current in the circuit reduces to zero.
ii) Threshold frequency is the minimum frequency of the incident radiation below which no emission of photoelectric takes place. The stopping potential (V0) and the threshold frequency (f0) are shown in [a diagram would be included here showing the relationship between stopping potential and frequency, typically a linear graph with a y-intercept representing the threshold frequency]. A description of the graph would be beneficial here, explaining that the slope is proportional to Planck's constant divided by the electron charge (h/e), and the y-intercept is the threshold frequency.