RBSE Class 12 Physics Chapter 11 — Dual Nature of Radiation and Matter: Most Repeated Questions (2013–2026)

The Phenomenon of ejection of electrons from the surface of a metal when light of suitable frequency strikes on it is called photoelectric effect. The emitted electrons are called photoelectrons

Only a few metals such as Potassium, Rubidium and Cesium in which electrons are loosely held by the nucleus shows this effect because their ionization energy is very low

W₀= Work function → Minimum energy required to eject electron (Threshold energy)

E= Energy of EM wave For Photoelectric effect:

E≥W₀

E=W₀+KE

hv=hv₀+KE

v= frequency of EM wave

v₀= threshold frequency = Minimum frequency required to eject electron

KE=hv-hv₀

KE=h(v-v₀)

KE=h(v-v₀)

OR

By writing Einstein's photoelectric equation, explain any two observations related to photoelectric effect

All solved questions for this chapter are in the full RBSE Physics PYQ book.

The wave theory of light fails to explain the photoelectric effect because it contradicts two major experimental observations:

(1) Existence of Threshold Frequency: Wave theory predicts that any frequency of light should eject electrons if the intensity is high enough, but experiments show no emission occurs below a specific threshold frequency ( V₀ ), regardless of intensity

(2) Kinetic Energy Dependence: Wave theory predicts that Kinetic Energy (KE) should increase with light intensity, but experimentally, KE is independent of intensity and depends only on the light's frequency

All solved questions for this chapter are in the full RBSE Physics PYQ book.

The threshold frequency ( V₀ ) is the minimum frequency of incident radiation required to cause photoelectric emission from a substance

All solved questions for this chapter are in the full RBSE Physics PYQ book.

Einstein's photoelectric equation

E=W₀+K.E

E=W₀+KE

Also,

E=W₀+qV₀

(∵V=W/q)

For electron

E=W₀+eV₀

hv=hv₀+eV₀

eV₀=hv-hv₀

V₀=(hv-hv₀)/e

All solved questions for this chapter are in the full RBSE Physics PYQ book.

The photoelectric effect is the phenomenon where electrons are ejected from a material's surface (usually metal) when it absorbs electromagnetic radiation of a sufficiently high frequency. This effect demonstrates the particle nature of light, where energy is transferred in discrete packets called photons

Effect of Potential on Photoelectric Current (at constant intensity):

​As the positive potential is increased, the current rises to a maximum saturation current ( I₀ )

​A negative potential, the stopping potential ( V₀ ), is required to reduce the current to zero, which is independent of intensity

All solved questions for this chapter are in the full RBSE Physics PYQ book.