An experimental setup of verification of photoelectric effect is shown in the diagram. The voltage across theelectrodes is measured with the help of an ideal voltmeter, and which can be varied by moving jockey 'j' on the potentiometer wire. The battery used in potentiometer circuit is of 20 V and its internal resistance is 2 Omega. The resistance of 100 cm long potentiometer wire is 8 Omega The photocurrent is measured with the help of an ideal ammeter. Two plates of potassium oxide of area 50 cm^(2) at separation 0.5 mm are used in the vacuum tube. Photo current in the circuit is very small so we can treat potentiometer circuit an independent circuit. The wavelengths of various colours is as follows : {:("Light",underset("Violet")(1),underset("Blue")(2),underset("Green")(3),underset("Yellow")(4),underset("Orange")(5),underset("Red")(6)),(lamda "in" Å rarr,4000-4500,4500-5000,5000-5500,5500-6000,6000-65000,6500-70000):}. When other light falls on the anode plate the ammeter reading remains zero till. jockey is moved from the end P to the middle point of the wire PQ. There after the deflection is recorded in the ammeter. The maximum kinetic energy of the emitted electron is