What is the photoelectric effect?

The photoelectric effect is the emission of electrons from a metal surface when light shines on it. Einstein explained it in 1905 by proposing that light consists of photons, each carrying energy E = hf. An electron is emitted only if the photon's energy exceeds the metal's work function (φ).

Why doesn't increasing intensity produce higher-energy electrons?

Increasing intensity means more photons per second, but each photon still carries the same energy (hf). More photons eject more electrons (higher current), but the maximum kinetic energy of each electron depends only on the photon frequency: KE_max = hf − φ. This was a key proof that light has particle-like properties.

What is stopping voltage in the photoelectric effect?

Stopping voltage (Vₛ) is the minimum reverse voltage needed to stop the most energetic emitted electrons from reaching the collector. It directly measures the maximum kinetic energy: eVₛ = KE_max = hf − φ. By plotting stopping voltage vs frequency, you can determine Planck's constant (h) and the work function (φ).

Photoelectric Effect Simulator

Shine light on a metal surface and observe electron emission. Explore how wavelength, intensity, and material affect the photoelectric effect — a cornerstone of quantum physics.

Light & Material

Presets

Wavelength = 300 nm

300

Intensity = 5

Stopping Voltage = 0 V

Material

Show

Photon beam Energy diagram KE vs f graph

Properties

Wavelength	300 nm
Frequency	--
Photon Energy	--
Material	Cesium
Work Function	2.1 eV
Threshold f	--
Threshold λ	--
Max KE	--
Stopping V	0 V
Emitted?	--

The Physics Behind It

Photoelectric Equations

Photon energy: E = hf = hc/λ
Max kinetic energy: KEₘₐₓ = hf − φ
Threshold frequency: f₀ = φ/h
Stopping voltage: eVₛ = KEₘₐₓ
h = 6.626 × 10⁻³⁴ J·s

Key Concepts

Photons are discrete packets of light energy; each carries energy E = hf
Work function (φ) is the minimum energy needed to free an electron from the metal surface
Intensity affects count of emitted electrons, not their maximum kinetic energy
Below threshold frequency, no electrons are emitted regardless of intensity — this proved light's particle nature

Photoelectric Effect Simulator

Light & Material

Properties

The Physics Behind It

Photoelectric Equations

Key Concepts

Related Visualizations

Diffraction Patterns

Ideal Gas Law

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