Photoelectric Effect Notes

Photoelectric Effect

Definition

The photoelectric effect is the emission of electrons when light shines on a material.

Historical Context

• Heinrich Hertz: Observed UV light increased spark size, terming it the photoelectric effect.

• Philipp Lenard:

  • Experimented with a vacuum tube, observing current only with UV light above a threshold frequency (f_0).

  • Threshold frequency (f_0) varies for different metals.

  • Increasing light intensity above f_0 increases photocurrent.

  • Experimented with voltage, defining stopping potential (V_s).

Einstein's Explanation (1905)

• Proposed light consists of energy quanta called photons, with energy E = hf.

Work Function and Kinetic Energy

• Photon ejects a single electron by transferring all its energy or none.

  • Work function (W): Minimum energy to remove an electron (W = hf_0).

  • Maximum kinetic energy (E_k) of ejected electrons.

Einstein's Photoelectric Equation

• Ek = hf - W = hf - hf0 = qV

Graphical Representation

• Gradient of lines equals Planck's constant (h).

  • X-intercept: threshold frequency (f_0).

  • Y-intercept: work function (W).

  • Equation: Ek = h(f - f0)