Photoelectric equation calculator

Worked example

Find Ek, the maximum kinetic energy of the photoelectrons. Given: frequency of the radiation f = 1.20 × 10¹⁵ Hz; work function φ = 4.00 × 10⁻¹⁹ J; Planck constant h = 6.63 × 10⁻³⁴ J s.

1. Write the equation
   h f = φ + E_k
2. Rearrange to make E_k the subject
   E_k = h f − φ
3. Constants used
   h = 6.63 × 10⁻³⁴ J s
4. Substitute the values
   E_k = (6.63 × 10⁻³⁴) × (1.2 × 10¹⁵) − (4 × 10⁻¹⁹)
5. Calculate
   E_k = 3.956 × 10⁻¹⁹ J
6. Give the answer to 3 significant figures
   E_k = 3.96 × 10⁻¹⁹ J

Symbols and units

Photoelectric equation: rearranged

• To find maximum kinetic energy of the photoelectrons: E_k = h f − φ
• To find frequency of the radiation: f = (E_k + φ) / h
• To find work function: φ = h f − E_k

Exam tip

If hf is less than the work function φ, no electrons are released however bright the light is.

Common questions

What is the formula for photoelectric equation?

The equation is h f = φ + Ek, where Ek is the maximum kinetic energy of the photoelectrons (J); f is the frequency of the radiation (Hz); φ is the work function (J); h is the Planck constant (J s).

What units should I use for photoelectric equation?

In SI units: maximum kinetic energy of the photoelectrons in J, Planck constant in J s, frequency of the radiation in Hz, work function in J. The calculator also accepts common alternatives such as kilometres, grams or minutes, and converts them for you.

How do I rearrange h f = φ + Ek?

Rearranging gives these forms: to find maximum kinetic energy of the photoelectrons: Ek = h f − φ. to find frequency of the radiation: f = (Ek + φ) / h. to find work function: φ = h f − Ek.