What Is the Photoelectric Effect?

The photoelectric effect is the emission of electrons from a material when it is illuminated by light of sufficiently high frequency. Each particle of light (photon) carries a discrete amount of energy. If a photon has enough energy to overcome the binding energy holding an electron in the material, that electron can be ejected from the surface as a photoelectron.

This phenomenon showed that light behaves not only as a wave but also as a stream of particles with quantized energy, helping to establish quantum mechanics. Albert Einstein explained the effect by proposing that the energy of a single photon is proportional to its frequency:

Photon energy relation: $E = h ν$

where:

$E$ is the energy of a photon (in joules, J)
$h$ is Planck's constant
$ν$ is the light frequency (in hertz, Hz)

When this energy exceeds the material's work function, electrons can be emitted with some kinetic energy. The calculator on this page uses these relationships to estimate photon energy, electron kinetic energy, and the stopping voltage for a given metal and light source.

Key Equations and Constants

The core physics of the photoelectric effect can be summarized with a few standard formulas and physical constants.

Key constants

Planck's constant: $h \approx 6.626 \times 10^{- 34} J·s$
Speed of light in vacuum: $c \approx 3.00 \times 10^{8} m/s$
Elementary charge: $e \approx 1.602 \times 10^{- 19} C$
Conversion between joules and electronvolts: $1 eV = 1.602 \times 10^{- 19} J$

Photon energy from frequency

When you know the frequency $ν$ of the light, the photon energy is:

E = h ν

Photon energy from wavelength

If you instead know the wavelength $λ$ , photon energy can be written as:

$E = \frac{h c}{λ}$

Since the calculator expects wavelength in nanometers (nm), the internal conversion is:

Convert nanometers to meters: $λ m = λ nm \times 10^{- 9}$
Then compute: $E = \frac{h c}{λ_{m}}$

Work function and threshold frequency

The work function $φ$ is the minimum energy needed to liberate an electron from the material's surface. In this calculator, you enter $φ$ in electronvolts (eV). The corresponding threshold frequency $ν_{0}$ (below which no electrons are emitted) is:

$h ν_{0} = φ \Rightarrow ν_{0} = \frac{φ}{h}$

Here, $φ$ is internally converted to joules using the factor $1 eV = 1.602 \times 10^{- 19} J$ .

Electron kinetic energy

Once photon energy exceeds the work function, the excess appears as kinetic energy $K$ of the emitted electrons:

$K = E - ϕ$

If both $E$ and $φ$ are expressed in electronvolts, the relation is especially simple:

$K_{eV} = E_{eV} - ϕ_{eV}$

If $K < 0$ , the photon energy is too low and no photoelectrons are emitted in the idealized model used here.

Stopping voltage

In a typical experiment, you can apply a reverse potential difference to stop emitted electrons from reaching the detector. The minimum potential needed to reduce the photoelectric current to zero is called the stopping voltage $V_{stop}$ . It is related to kinetic energy by:

$K = e V_{stop}$

When kinetic energy is expressed in electronvolts, it is numerically equal to the stopping voltage in volts:

$K_{eV} = V_{stop} (V)$

The calculator reports this stopping voltage so you can connect the abstract energy values to a measurable electrical quantity.

How to Use the Photoelectric Effect Calculator

This tool is designed for quick exploration of how different materials and light sources influence photoelectron emission. You can use it for classroom demonstrations, homework checks, or simple lab planning.

Enter the work function $φ$ in eV.
- Typical metallic work functions are between about 2 eV and 5 eV.
- Use a value from a textbook, data table, or your experiment notes.
Provide either the light frequency $ν$ in Hz or the wavelength $λ$ in nm.
- You may enter frequency if that is how your light source is specified.
- You may instead enter wavelength in nanometers, which is common for lasers and LEDs.
- If you know both, you only need to enter one; the calculator can work from either input.
- For very large or small values, you can use scientific notation, such as 5e14 Hz or 400 nm.
Run the calculation. The tool computes photon energy, kinetic energy, and the corresponding stopping voltage.

The main outputs you should expect are:

Photon energy in joules (J) and electronvolts (eV)
Kinetic energy of emitted electrons in electronvolts (eV)
Stopping voltage in volts (V), which equals the kinetic energy in eV in this ideal model
An indication of whether emission occurs at all (if the photon energy is below the work function, kinetic energy is taken as zero and no photoelectrons are predicted)

Worked Example

This example shows how the calculator's underlying steps might look if you performed them by hand. Suppose you illuminate sodium (approximate work function $ϕ \approx 2.3 eV$ ) with violet light of wavelength $λ = 400 nm$ .

1. Convert wavelength to photon energy

First convert wavelength to meters:

$λ = 400 nm = 400 \times 10^{- 9} m = 4.00 \times 10^{−7} m$

Then compute photon energy using $E = \frac{h c}{λ}$ :

$E = \frac{(6.626 \times 10^{- 34} J·s) (3.00 \times 10^{8} m/s)}{4.00 \times 10^{- 7} m}$

Multiplying the numerator:

$6.626 \times 10^{- 34} \times 3.00 \times 10^{8} \approx 1.988 \times 10^{- 25} J·m$

Now divide by $4.00 \times 10^{- 7} m$ :

$E \approx \frac{1.988 \times 10^{- 25}}{4.00 \times 10^{- 7}} J = 4.97 \times 10^{- 19} J$

2. Convert photon energy to eV

Use the conversion $1 eV = 1.602 \times 10^{- 19} J$ :

$E_eV = \frac{4.97 \times 10^{- 19} J}{1.602 \times 10^{- 19} J/eV} \approx 3.10 eV$

3. Subtract the work function

Now subtract the work function of sodium:

$K_{eV} = E_{eV} - φ_{eV} = 3.10 eV - 2.3 eV = 0.8 eV$

So in this idealized scenario, emitted electrons have a maximum kinetic energy of about 0.8 eV.

4. Determine the stopping voltage

Because $1 eV = e \times 1 V$ , the kinetic energy in eV is numerically equal to the stopping voltage in volts:

$V_{stop} \approx 0.8 V$

In other words, you would need to apply approximately 0.8 V of reverse bias to stop the photoelectrons produced by 400 nm light on sodium. The calculator carries out all of these steps for you automatically.

Comparison of Typical Work Functions

Different materials require different photon energies to emit electrons. The table below lists a few common metals, their approximate work functions, and the corresponding threshold wavelength (longest wavelength that can still cause emission).

Material	Work function $φ$ (eV)	Threshold wavelength $λ_{0}$ (nm, approx.)	Threshold frequency $ν_{0}$ ( $10^{14}$ Hz, approx.)
Cesium (Cs)	2.1	~590	~5.1
Sodium (Na)	2.3	~540	~5.6
Calcium (Ca)	2.9	~430	~7.0
Zinc (Zn)	4.3	~290	~1.0
Copper (Cu)	4.7	~260	~1.2

The threshold wavelength values are estimated using the relation

$λ 0 = \frac{h c}{φ}$

with $φ$ converted from eV to joules. For wavelengths longer than $λ_{0}$ , photon energy is lower than the work function and the idealized model predicts no photoemission. You can use these values as starting points when choosing example inputs for the calculator.

Interpreting the Results

When you run the calculator, you will typically see:

Photon energy (J and eV): This tells you how energetic each incident photon is. Higher photon energy increases the chance of surpassing the work function.
Kinetic energy of electrons (eV): This is the maximum kinetic energy predicted for emitted electrons in the ideal model. In practice, some electrons may have lower energies due to how they are bound inside the material.
Stopping voltage (V): This is the potential difference that would just stop the most energetic photoelectrons from reaching the anode in a typical photoelectric experiment.

If the calculator reports a negative or zero kinetic energy, it means that the photon energy is not sufficient to overcome the work function. Under those conditions, the model predicts no photoelectric emission, regardless of how intense the light is. Increasing intensity would only increase the number of incident photons, not their individual energies.

Limitations and Assumptions

The calculator uses a simplified, textbook-style model of the photoelectric effect. Keep the following assumptions and limitations in mind when interpreting the results:

Ideal, clean surface: Real materials may have oxide layers, impurities, or surface roughness that change the effective work function. The calculator assumes a perfectly clean and uniform surface.
Single-photon emission: The model assumes that each photoelectron is produced by a single photon, with no multiphoton processes. At very high intensities or with ultrashort pulses, more complex behavior can occur.
Monochromatic light: The formulas assume that the light has a single well-defined wavelength or frequency. Real sources (like lamps or the sun) often have a spectrum of wavelengths; the calculator does not model full spectra.
No space-charge or field effects: In intense beams or in small experimental geometries, mutual repulsion between electrons and electric fields in the apparatus can modify the observed energies. These effects are not included.
Maximum kinetic energy only: Actual experiments measure a distribution of electron energies. The value returned by the calculator corresponds to the maximum predicted kinetic energy for electrons escaping the surface.
Educational and estimation use: Values from this calculator are meant for learning, quick checks, and approximate planning of simple experiments. They are not a substitute for detailed experimental design or precision metrology.

By being aware of these assumptions, you can better judge when the outputs are appropriate for your needs and when a more sophisticated model or direct measurement would be required.

Photoelectric Effect Calculator

What Is the Photoelectric Effect?

Key Equations and Constants

Key constants

Photon energy from frequency

Photon energy from wavelength

Work function and threshold frequency

Electron kinetic energy

Stopping voltage

How to Use the Photoelectric Effect Calculator

Worked Example

1. Convert wavelength to photon energy

2. Convert photon energy to eV

3. Subtract the work function

4. Determine the stopping voltage

Comparison of Typical Work Functions

Interpreting the Results

Limitations and Assumptions

Embed this calculator

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