An experimental setup of verification of photoelectric effect is shown in the diagram. The voltage across the electrodes 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):}`.
Which of the following colour may not give photoelectric effect from this cathode :

Options

A. Green
B. Violet
C. Red
D. Orange

Answer

C

Explanation

The range of wavelength for red light is beyond the wavelength of incident light.