Einstein’s photoelectric equation
The theoretical explanation of the photoelectric effect based on the quantum nature of light and its implications.
What is Einstein’s photoelectric equation?
The emission of electrons from a material, usually a metal, when light shines on it.
Key formula / rule: Photon Energy
Key points
- Explain the photoelectric effect using Einstein's theory.
- State and apply Einstein's photoelectric equation.
- Differentiate between photon energy, work function, and kinetic energy.
- Understand the role of frequency and intensity in the photoelectric effect.
Common exam trap
Confusing photon energy with light intensity.
Definitions
- Term
Photoelectric Effect
- Meaning
The emission of electrons from a material, usually a metal, when light shines on it.
- Term
Photon
- Meaning
A quantum of electromagnetic radiation; a discrete packet of light energy.
- Term
Work Function (Φ)
- Meaning
The minimum energy required for an electron to escape from the surface of a metal.
- Term
Threshold Frequency (ν₀)
- Meaning
The minimum frequency of incident radiation below which the photoelectric effect does not occur, regardless of the intensity.
- Term
Threshold Wavelength (λ₀)
- Meaning
The maximum wavelength of incident radiation below which the photoelectric effect does not occur, regardless of the intensity.
- Term
Maximum Kinetic Energy (KEmax)
- Meaning
The highest kinetic energy possessed by the photoelectrons emitted from the metal surface.
Learning objectives
Explain the photoelectric effect using Einstein's theory.
State and apply Einstein's photoelectric equation.
Differentiate between photon energy, work function, and kinetic energy.
Understand the role of frequency and intensity in the photoelectric effect.
Define threshold frequency and threshold wavelength.
Formulae
- Name
Photon Energy
- Note
Where h is Planck's constant, ν is frequency, c is the speed of light, and λ is wavelength.
- Expression
E = hν = hc/λ
- Name
Einstein's Photoelectric Equation
- Note
KEmax is the maximum kinetic energy of emitted electrons, hν is the energy of incident photon, and Φ is the work function of the metal.
- Expression
KEmax = hν - Φ
- Name
Work Function in terms of Threshold Frequency
- Note
ν₀ is the threshold frequency, the minimum frequency of incident light required for photoelectric emission.
- Expression
Φ = hν₀
- Name
Work Function in terms of Threshold Wavelength
- Note
λ₀ is the threshold wavelength, the maximum wavelength of incident light required for photoelectric emission.
- Expression
Φ = hc/λ₀
Prerequisites
Basic understanding of light as electromagnetic waves.
Concept of energy and kinetic energy.
Understanding of atomic structure and electrons.
Familiarity with basic algebra.
Common mistakes
Confusing photon energy with light intensity.
Assuming photoelectric emission occurs for any frequency if intensity is high.
Incorrectly applying the equation when hν < Φ (no emission).
Forgetting that KEmax is the *maximum* kinetic energy.
Keywords
Photoelectric effect
Einstein's equation
Photon
Work function
Threshold frequency
Kinetic energy
Planck's constant
Quantum nature of light
Practice preview
A metal surface has a work function of 2.3 eV. If photons of energy 6.1 eV are incident on it, what is the maximum kinetic energy of the emitted photoelectrons?…
medium
Consider two metals, A and B, with work functions Φ_A and Φ_B respectively. If Φ_A < Φ_B, and both metals are illuminated by monochromatic light of the same frequency ν, which of the following statements is true regardin…
hard
According to Einstein's photoelectric equation, the kinetic energy of the emitted electrons is given by:…
easy