# Wave Particle Duality

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## Wave Particle Duality

So light - which we thought was a wave - has got the properties of particles in certain situations.

The answer is - **it is both!** You have to treat it like a wave to explain what happens to it as it travels (propagates) and treat it like a particle to explain what happens when it arrives (impinges) at a surface.

If waves sometimes behave like particles, couldn't the reverse be true? A man called **Count Louis de Broglie** thought so. He did the experiments that showed that you could make particles like electrons diffract. Now that's what waves do, not particles!

Since then, other particles (protons, neutrons and alpha particles) have been shown to have wave properties too.

To explain the wave like behaviour of particles, de Broglie developed an equation that answers the question "If electrons are behaving like waves, what's their wavelength?"

**The answer is:**

**Where;**

**λ** = the de Broglie wavelength, which you could use in wave equations like the diffraction grating equation, for example.

**h** = Planck's constant

**p** = the momentum of the particle (mass x velocity).