Light from a hydrogen discharge tube is incidenton the cathode of a photoelectric cell. The work function of the cathode surface is 4.2 eV. In other to reduce the photocurrent to zero, the boltage of the anode relative to the cathode must be made

Options

A. `-4.2 V`
B. `-9.4V`
C. `-17.8V`
D. `+9.4V`

Answer

B

Explanation

`eV_0=E-phi`
`V_0 = ((13.6 4.2)eV)/e = 9.4V`
Potential at anode = -9.4 V.