Apparatus:
Photocell, battery, key, micro ammeter or galvanometer, electric lamp, ruler and conne wires.
Theory:
In photocell an electric current is produced by the photo electric effect. It consists of t electrodes a plan cathode coated with a suitable photo-sensitive material and anode that is maintain at positive potential with respect to the cathode. The anode attracts the phot electrons liberated by the cathode. These electrodes are arranged in an evaluated glas envelope. The current passing through the cell is a measure of light intensity incident on the cathode.
Procedure:
1. Arrange the apparatus as shown in figure and put a lamp a distance of 80 cm from the photo cell.
2. Note the deflection in galvanometer.
3. change the distance d to 70, 60,50 cm…. and obtain the value of for each error spending reading.
4.Record the observation in the table and plot a graph between
and it is a straight line.
Observations &Calculations
Result:
Since d is constant. The graph between I and is straight line. This shows that photo electric rent varies directly with the intensity of light.
Precautions:
- The voltage applied to the electrodes of the photo cell should not be more than rated value. Use sensitive galvanometer or micro ammeter as current produced in photocell is very small.
- The distance of light source be changed in regular steps.
- A point source is advised so that inverse square law holds good.
Viva voce
Q1: What is photo electric effect?
Ans: The phenomenon in which light of suitable frequency falls on metal surface and electrons emit from metal surface and electrons emit from metal surface is called photoelectric effect.
Q2: What are photo electrons?
Ans: The electrons which are emitted by metal surface when light of suitable frequency falls on mental it are called photo electrons.