De Broglie Wavelength Calculator

Created by Bogna Szyk
Reviewed by Steven Wooding
Last updated: Dec 25, 2022

This de Broglie wavelength calculator will help you describe the wave-particle duality of matter. According to this principle, we can analyze light as waves, explaining its properties such as refraction. On the other hand, light must be made of particles (called photons) if we want to understand the photoelectric effect. De Broglie stated that every particle could be described as having a particular wavelength and formulated the famous de Broglie equation. If you want to know the de Broglie wavelength of an electron or a photon, keep reading!

🙋 You can read about the phenomena described above in the photoelectric effect calculator and the index of refraction calculator.

What is the de Broglie equation?

According to de Broglie, a beam of particles of some mass can behave as a matter wave. Its wavelength is related to the mass and velocity of the particle: λ = h / (m × v),
where:

  • m is the mass of the particle;
  • v is the velocity of the particle, and
  • h is the Planck constant, equal to 6.6261×10-34 Js.

The units of mass

The mass of particles is usually given in kilograms, but using scientific notation since the numbers are small. In the calculator, use the drop-down menu to select the exponent of the mass. For reference, these are the value of the electron rest mass (me) and the atomic mass unit (u), which is an average of the proton and neutron masses.

1 me = 9.10938356 × 10-31 kg

1 u = 1.660538921 × 10-27 kg

What is the de Broglie wavelength of an electron?

Let's find the de Broglie wavelength of an electron traveling at 1% of the speed of light.

  1. The mass of an electron is 1 me, or
    9.10938356*10-31 kg
  2. The speed of this electron is
    299,792,458 m/s / 100 = 2,997,924.58 m/s.
  3. Multiplying the mass and speed, we obtain the momentum:
    p = mv = 2.7309245 × 10-24 kg·m/s
  4. Dividing the Planck constant by p, we obtain the de Broglie wavelength:
    h/p = 6.6261*10-34 / 2.7309245*10-24 = 2.426 × 10-10 m.
  5. Hence, the de Broglie wavelength of our electron is 0.24 nm.

How to calculate the de Broglie wavelength of a photon?

Since a photon's rest mass is zero, you might be wondering how to use our de Broglie wavelength calculator to find the de Broglie wavelength of a photon. Thanks to wave-particle duality, a photon does have a momentum associated with it. The value of this momentum can be used to calculate the de Broglie wavelength of the photon.

A question asks you to find the de Broglie wavelength of a photon which has a momentum of 6.8 × 10-35 kg·m/s. Let's see how to use our calculator to answer this question.

  1. Click on the unit changer menu of the momentum row and select x10-35 from the list.
  2. Enter 6.8 into the momentum row. You've now entered the correct value for the momentum of the photon.
  3. You will see the result for the wavelength in nanometers by default. As it is a huge value, you'll probably want to change the units to something more manageable, such as meters. The result is 9.74 m, rounding to 3 significant figures. This type of rounding is described in the significant figures calculator.

FAQ

What is the unit of the de Broglie wavelength?

The unit in which the de Broglie wavelength is expressed is meters. Since the de Broglie wavelength is usually very, very small, we most often express this value in nanometres.

How do I calculate the de Broglie equation?

To determine the de Broglie wavelength of a particle given its mass and velocity, you need to:

  1. Multiply the velocity by mass. Their product is the particle's momentum.
  2. Divide Planck's constant by the momentum found in Step 1.
  3. The result you've got is exactly the de Broglie wavelength of your particle. Congrats!
Bogna Szyk
Rest mass (m)
×10⁻³¹
kg
Velocity (v)
m/s
Momentum (p)
×10⁻²⁴
kg·m/s
Wavelength (λ)
nm
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