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Photon energy calculator

A-level Nuclear and particles

The energy of one photon of electromagnetic radiation of a given frequency.

E = h f

This free calculator is for A-level physics. Choose the quantity you want to find, enter the other values with their units, and it shows the working in the layout used in exams, with the answer to the number of significant figures you choose. The values shown are an example. Change them to your own.

Quantity to find

EPhoton energy to find 3.98 × 10⁻¹⁹ J

hPlanck constant constant J s

fFrequency

Significant figures

Working

Write the equation
E = h f
Constants used
h = 6.63 × 10⁻³⁴ J s
Substitute the values
E = (6.63 × 10⁻³⁴) × (6 × 10¹⁴)
Calculate
E = 3.978 × 10⁻¹⁹ J
Give the answer to 3 significant figures
E = 3.98 × 10⁻¹⁹ J

Worked example

Find E, the photon energy. Given: frequency f = 6.00 × 10¹⁴ Hz; Planck constant h = 6.63 × 10⁻³⁴ J s.

Write the equation
E = h f
Constants used
h = 6.63 × 10⁻³⁴ J s
Substitute the values
E = (6.63 × 10⁻³⁴) × (6 × 10¹⁴)
Calculate
E = 3.978 × 10⁻¹⁹ J
Give the answer to 3 significant figures
E = 3.98 × 10⁻¹⁹ J

Symbols and units

Symbol	Quantity	SI unit
E	Photon energy	J
h	Planck constant (constant)	J s
f	Frequency	Hz

Photon energy: rearranged

To find photon energy: E = h f
To find frequency: f = E / h

Exam tip

Use the unit selector to give the answer in eV. To convert by hand, divide joules by 1.60 × 10⁻¹⁹.

Common questions

What is the formula for photon energy?

The equation is E = h f, where E is the photon energy (J); f is the frequency (Hz); h is the Planck constant (J s).

What units should I use for photon energy?

In SI units: photon energy in J, Planck constant in J s, frequency in Hz. The calculator also accepts common alternatives such as kilometres, grams or minutes, and converts them for you.

How do I rearrange E = h f?

Rearranging gives these forms: to find photon energy: E = h f. to find frequency: f = E / h.

Practise photon energy questions

Include unit conversions (km, g, minutes…)

Press the button for a question with random numbers. Work it out on paper first, then type your answer.

Read the full explanation on the Photon energy from frequency formula page. More nuclear and particles equations: Photon energy from wavelength, Photoelectric equation, de Broglie wavelength, Radioactive decay and half-life, Activity and decay constant, Half-life and decay constant, Mass–energy equivalence. See the full list on the a-level physics equation calculator page.