Question

Photons with energy 5 eV are incident on a cathode C in a photoelectric cell. The maximum energy of emitted photoelectrons is 2 eV. When photons of energy 6 eV are incident on C, no photoelectrons will reach the anode A, if the stopping potential of A relative to C is
1. +3 V
2. +4 V
3. -1 V
4. -3 V

Answer 1

Correct Answer - Option 4 : -3 V

Concept:

According to Einstein’s photoelectric equation maximum kinetic energy of photoelectrons,

Incident energy = work function + K.E

KE_max = E_v – ϕ

Calculation:

Case 1: When 5eV is incident

5eV = W + 2eV

W = 3eV

Case 2: When 6eV is incident

6 = 3 + K.E

K.E = 3 eV

To stop the electron, negative potential is required with magnitude of the voltage as (3V)

Hence stopping potential = -3V