Wave-particle duality
Light behaves like a wave and like a stream of particles. Matter such as electrons also behaves like a wave. The de Broglie wavelength is λ = h/mv, so heavy, fast objects have wavelengths too small to notice.
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Analogy
Like a coin that looks like a circle from the front and a thin line from the side. Same object, different view.
Example
m = 9.11×10⁻³¹ kgλ = h/mvλ = 6.626×10⁻³⁴ / 9.11×10⁻²⁵λ = 7.3×10⁻¹⁰ m (0.73 nm)
In practice
Electron microscopes work because fast electrons have very short wavelengths, so they can show much finer detail than visible light.
Practice
Flashcards
- What is the de Broglie wavelength?λ = h/mv. It links a particle's momentum to its wavelength.
Questions people ask
Why don't we see a thrown ball behave like a wave?
A ball has a huge mass compared with an electron. In λ = h/mv, a large m makes the wavelength unimaginably small, around 10⁻³⁴ m for a thrown ball. No experiment can detect a wave that small, so the ball acts like a plain particle.
What evidence shows electrons act as waves?
Electrons fired at a thin crystal make a pattern of bright and dark rings, called diffraction. Only waves make this kind of pattern, because they add up in some places and cancel in others. The rings match the wavelength given by de Broglie's equation.