(a) Define the terms, (i) threshold frequency and (ii) stopping potential in photoelectric effect.
(b) Plot a graph of photocurrent versus anode potential for a radiation of frequency v and intensities I1 and I2 (I1 < I2).
Answers
THRESHOLD FREQUENCY is the minimum amount of energy required by a photon to ionize a given atom in the photo electric effect.
1)Photo electric effect is a process in which a photon or a particle strikes a metal surface and in doing so removes an electron from the outer shell of the atom.The photon transfers it's momentum to the electron.
2)However electrons are bound to the atom in a particular energy state which we call a shell so in order to completely remove an electron the photon must have energy which is greater than the binding energy of the electron .This is known as threshold frequency.
STOPPING POTENTIAL:The potential at which no electron reaches the collector plate and hence no current flows through the circuit is known as stopping potential.
3)When an electron is emitted from the metal surface it is accelerated towards a collector plate .
4)This is done by applying a positive potential on the collector plate.
5)However when negative potential is applied on the collector plate the emitted electrons are repeled.
6)When electrons are emitted they have some kinetic energy so they are able to come the repulsive force from the collector plate and reach their .
7)However when the negative potential at the collector plate is further increased the electrons are not able to reach the collector plate and the current seizes to flow.The potential at which this takes place is known as stopping potential.