Light of a fixed frequency and intensity falls on the emitter plate o…

The correct answer is Option (3) → Three

Changing the emitter changes only the work function \( \phi_0 \). The light is the same, so every photon reaching the plate has the same energy and momentum as before.

The quantities that change are:

• Threshold frequency — \( \nu_0=\phi_0/h \), so a larger work function means a higher threshold frequency.

• Maximum kinetic energy — \( K_{max}=h\nu-\phi_0 \) is smaller, since more of the same photon energy is used up in escaping.

• Stopping potential — \( eV_0=K_{max} \), so it falls along with the maximum kinetic energy.

The quantities that do not change are:

• Energy of each photon — \( E=h\nu \) depends on the frequency of the light alone.

• Momentum of each photon — \( p=h\nu/c \) also depends on the frequency alone.

Number of quantities that change = 3

NCERT (2026-27):
Einstein’s Photoelectric Equation: Energy Quantum of Radiation – “… the greater the work function φ₀, the higher the minimum or threshold frequency ν₀ needed to emit photoelectrons.”

Summary – “4. The stopping potential (V_o) depends on (i) the frequency of incident light, and (ii) the nature of the emitter material. For a given frequency of incident light, it is independent of its intensity. The stopping potential is directly related to the maximum kinetic energy of electrons emitted: e V₀ = (1/2) m v²_max = K_max.”

Particle Nature of Light: the Photon – “(iii) All photons of light of a particular frequency ν, or wavelength λ, have the same energy E (=hν = hc/λ) and momentum p (= hν/c= h/λ), whatever the intensity of radiation may be.”