3.2.2.4 Particles and Radiation: Wave-particle duality

Question 1

What is the evidence that light is a wave?

Answer 1

It can diffract (a property only of waves)

Question 2

What is the evidence that light is a particle?

Answer 2

If a photon of light is a discrete bundle of energy, it can interact with an electron in a one-to-one way. All the energy of the photon is given to one electron (?)

Question 3

What is the de Broglie equation?

Answer 3

lambda = h/(mv)

• it relates wave property (wavelength) to a moving particle property (momentum)

Question 4

Describe electron diffraction

Answer 4

Electrons are accelerated to high velocities in a vacuum and then passed through a graphite crystal, as they pass through the spaces in the crystal, they diffract like waves passing through a narrow slit and produce a pattern of rings, providing evidence that electrons have wave-like properties.

Question 5

How do electron microscopes work?

Answer 5

Shorter wavelength gives smaller diffraction effects. Diffraction effects blur details on an image. Light blurs out detail more than ‘electron waves’, so an electron microscope can resolve finer detail.