Einstein's Photoelectric Equation

Einstein's Photoelectric Equation

What is it?

Einstein explained the photoelectric effect using conservation of energy for individual photons.

In simple words

• Einstein’s equation quantitatively explains photoelectric observations.

Full school-level explanation

Einstein explained the photoelectric effect using conservation of energy for individual photons.

Stopping Potential

A photon has energy: E=hf When it interacts with an electron, part of this energy is required to release the electron from the material. This minimum energy is: work function `φ` Remaining energy becomes maximum photoelectron kinetic energy: hf = φ + K_max Therefore: K_max = hf−φ Since: φ=hf₀ we get: K_max = h(f−f₀) If stopping potential `V_s` just stops the fastest photoelectrons: K_max=eV_s Therefore: eV_s=hf−φ

Graph

A graph of `K_max` against `f` has: slope: h and frequency-axis intercept: f₀

Formula / Key Relation

**hf=φ+K_max** **K_max=h(f−f₀)** **K_max=eV_s**

Remember

• K_max=eV_s
• eV_s=hf−φ
• h
• f₀
• hf=φ+K_max
• K_max=h(f−f₀)
• K_max=eV_s

Deeper understanding

Go deeper on Einstein's Photoelectric Equation: connect the definition to reasons, relationships, exceptions, and exam wording.

Common mistakes

Exam focus

`hf = φ + Kmax`

Exam focus

Quick revision

• K_max=eV_s
• eV_s=hf−φ
• h
• f₀
• Stopping Potential: A photon has energy: E=hf When it interacts with an electron, part of this energy is required
• Graph: A graph of `K_max` against `f` has: slope: h and frequency-axis intercept: f₀

For long answers on Einstein's Photoelectric Equation: define clearly → explain the main parts → give one example → state one exam caution.