The energy of a photon is the sum of the kinetic energy (of an electron released with the help of the photon) and the work function of the illuminated material. From the photon energy, the frequency of the light can be determined:$$ f~=~ \frac{ W_{\text p} }{ h } $$

Light frequency

\( f \) Unit \( \mathrm{Hz} \)

Frequency of the used light source. If you multiply light frequency with Planck's constant \(h\), you obtain the energy \(W_{\text p}\) of a photon.

Work function

\( W \) Unit \( \mathrm{J} \)

Work function is the energy that must be spent to knock an electron out of a solid (e.g. a metal plate). It is usually given in units of "eV" (electron volt) and can be calculated with the help of the cutoff frequency \( f_0 \):$$ W = h\, f_0 $$

Cutoff frequency

\( f_0 \) Unit \( \mathrm{Hz} \)

Cutoff frequency is the minimum frequency of light necessary to knock out electrons. Multiply it by the Planck's constant \(h\) to obtain the work function: \(W = h \, f_0 \).

Velocity

\( v \) Unit \( \frac{\mathrm m}{\mathrm s} \)

Maximum speed of an electron knocked out by a photon. If the material is illuminated by photons with a larger photon energy \(W_{\text p}\) ( at constant work function \(W\)), then also the electron speed becomes larger.

Electron mass

\( m_{\text e} \) Unit \( \mathrm{kg} \)

Rest mass of the electron. It is a physical constant with the value:$$ m_{\text e} = 9.109 \cdot 10^{-31} \, \mathrm{kg} $$

Planck's constant

\( h \) Unit \( \mathrm{Js} \)

Planck's constant is a physical constant of quantum mechanics and has the value:$$ h = 6.626 \, 070 \, 15 \,\cdot 10^{-34}\, \, \mathrm{Js} $$

You must have JavaScript enabled to use this form.

Give feedback

Hey! I am Alexander, the physicist and author here. It's important to me that you are satisfied when you come here to get your questions answered and problems solved. But since I don't have a crystal ball, I depend on your feedback. That way I can eliminate mistakes and improve this content so that other visitors can benefit from your feedback.

How satisfied are you?

Very nice!

If there is anything you would like to see improved, please send me a message below. I would be very happy if you support the project.

Hmm...

Would you mind telling me what you were missing? Or what you didn't like? I take every feedback to heart and will adapt and improve the content.

What's the trouble?

Do not be disappointed, I can certainly help you. Just send me a message what you actually wanted to find here or what you don't like. I really take your feedback seriously and will revise this content. If you are very disappointed, explain your concern in the feedback and leave your email and I will try to help you personally.