Photon Energy and Photoelectric Effect Calculator: Wavelength, Frequency, Stopping Voltage and De Broglie Wavelength

Photons, the photoelectric effect and matter waves, with the working.

Calculated from standard textbook formulas, with every step shown. The formulas are fixed, so the working does not need checking: what matters is the numbers you type in. Use these calculators only if you are competent to choose the inputs (loads, material strength, dimensions, supports) and check your units and assumptions. For learning and checking your own working: design and sign-off are for a qualified engineer. Drafting Central does not store the numbers you type.

How this calculator works

Choose photon, photoelectric effect or de Broglie wavelength.

For a photon enter the wavelength, frequency or energy. For the photoelectric effect enter the wavelength of the light and pick the metal. For a particle pick it and give its speed or energy.

The calculator gives the energies in eV and joules, the wavelengths, the stopping voltage and the threshold values.

Formulas used

  • E = hf = \frac{hc}{\lambda}
  • E_k = hf - \phi
  • eV_0 = E_k
  • \lambda = \frac{h}{p} = \frac{h}{mv}

Worked example

With the default numbers in the calculator above:

  1. Energy of the photon: 2.47968 eV (3.9729e-19 J)
  2. Wavelength: 500 nm
  3. Frequency: 599.585 THz (5.9958e+14 Hz)
  4. Momentum of the photon: 1.3252e-27 kg m/s
  5. Part of the electromagnetic spectrum: visible light

Change the numbers in the calculator to see the full working, every step, for your own case.

A second worked example

A different case, with these numbers: What do you want? Photoelectric effect.

  1. Energy of each photon: 4.13281 eV
  2. Work function of the metal (the energy needed to free an electron): 2.75 eV
  3. Threshold wavelength and frequency (the longest wavelength that works): 450.852 nm and 664.947 THz
  4. Maximum kinetic energy of the emitted electrons: 1.38281 eV (2.2155e-19 J)
  5. Stopping potential (the voltage that stops the fastest electrons): 1.38281 V
  6. Speed of the fastest electrons: 6.9744e+5 m/s

Common questions

What is the photoelectric effect?

Light above a certain frequency knocks electrons out of a metal. Each photon gives all its energy to one electron.

What is the work function?

The minimum energy needed to free an electron from the metal surface.

Why does brighter light not give faster electrons?

The energy of each photon depends on frequency only. A brighter light has more photons, so it releases more electrons, not faster ones.

What is the de Broglie wavelength?

The wavelength of a moving particle, h divided by its momentum. It shows up for electrons but is far too small to notice for everyday objects.

Related calculators

Got a question about this? Ask an engineering question and get a plain-language answer with references.

Further reading: Any first-year physics text (quantum physics). Planck constant and electron charge from the 2019 SI definitions.

Need a calculator we do not have?

Tell us what you would like to calculate. We read every request and build the most asked-for ones.

We store your request (and your email if you give it) to decide what to build. We do not store the numbers you type into calculators.

Embed this calculator on your own page

Copy this code into your page. The calculator runs inside the frame and links back to Drafting Central.

Need this drawn, designed or checked?

Drafting Central is a mechanical engineering and drafting business working with customers across Australia and around the world. A calculator gives you the numbers; we can turn them into drawings and designs.

Need help with a real project?

Talk to Drafting Central →

← All engineering calculators