Photon with energy 5eV are incident on a cathode C of a photoelectric cell. The maximum energy of the photoelectron emitted is 2eV. When photons of energy 6eV are incident on C, no photoelectron will reach the anode A if stopping potential of A relative to C is

Photon with energy 5eV are incident on a cathode C of a photoelectric cell. The maximum energy of the photoelectron emitted is 2eV. When photons of energy 6eV are incident on C, no photoelectron will reach the anode A if stopping potential of A relative to C is Correct Answer -3V

CONCEPT:

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Photoelectric effect:

• When the light of a sufficiently small wavelength is incident on the metal surface, electrons are ejected from the metal instantly. This phenomenon is called the photoelectric effect.

Stopping potential:

• It is defined as the potential required to stop the ejection of an electron from a metal surface when the incident beam of energy is greater than the work function of the metal.

Work function:

• It is the minimum amount of energy required so that metal emits an electron. It is represented by ϕ. 
• Einstein’s equation of photoelectric equation:

⇒ KEmax = E - ϕo

Where E = incident energy of photons, ϕo = work function, and KE = maximum kinetic energy of electrons.

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, a negative potential is required whose magnitude is the equivalent voltage is (3V)

Hence stopping potential = -3V