Class 12 Physics Dual Nature of Radiation and Matter Notes | Photoelectric Effect for JEE & NEET

Work function is the minimum energy (in eV) needed to eject an electron from a metal surface. Caesium has the lowest work function at approximately 2.0 eV, making it the most sensitive metal to light. Metals with low work functions are used in photoelectric devices like photocells and solar panels.

Einstein's photoelectric equation is KE_max = hν − φ, where KE_max is the maximum kinetic energy of the emitted electron, h is Planck's constant, ν is the frequency of incident light, and φ is the work function of the metal. It tells you exactly how much energy an electron gains after overcoming the metal's binding energy.

The photoelectric effect is the release of electrons from a metal surface when light hits it. Only light above a specific minimum frequency — called the threshold frequency — can eject electrons. The number of electrons ejected increases with light intensity, but their maximum kinetic energy depends only on the frequency of light. Einstein explained this using photons in 1905.

In JEE Main, Dual Nature of Radiation and Matter typically contributes 1–2 questions (4–8 marks) per paper. In NEET, it contributes 2–3 questions (8–12 marks). High-yield topics are Einstein's photoelectric equation, stopping potential graphs, and de Broglie wavelength calculations. Consistent practice with previous year papers significantly improves accuracy in this chapter.

de Broglie wavelength (λ) is the wavelength associated with any moving particle, given by λ = h/mv, where h is Planck's constant, m is mass, and v is velocity. For an electron accelerated through potential V, the formula becomes λ = h/√(2meV). This concept proved particles have wave properties.

Stopping potential (V₀) is the minimum reverse voltage applied to a photoelectric cell that reduces photocurrent to zero. It equals KE_max/e, where e is the electron charge. Stopping potential depends on the frequency of incident light and the metal used — it does not change with light intensity.