An experimental setup of verification of photoelectric effect is shown in the diagram. The voltage across the electrode is measured with the help of an ideal voltmetar, 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 `2omega`. The resistance of `100 cm` long potentiometer wire is `8 omega`. The photo current 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 indepdent circuit. The wavelength of various colours is as follows :
_E01_156_Q01.png)
`|{:("Light",underset("Violet")(1),underset("Blue")(2),underset("Green")(3),underset("Yellow")(4),underset("Orange")(5),underset("Red")(6)),(lambda "in" Årarr,4000-4500,4500-5000,5000-5500,5500-6000,6000-6500,6500-7000):}|`
When radiation falls on the cathode plate a current of `2muA` is recorded in the ammeter. Assuming that the vecuum tube setup follows ohm's law, the equivalent resistance of vacuum tube operating in this case when jockey is at end P.
