4.5.3 - Wave Particle Duality

Question 1

What is wave-particle duality?

Answer 1

The idea that a single entity/quantum object (such as, light and electrons) can exhibit both wave-like and particle-like properties. It is used to best explain their behaviour in different situations.

Question 2

What are the two models that can be used to explain the behaviour of radiation?

Answer 2

• Particle Model

- Wave Model

Question 3

Which model best explains diffraction and interference?

Answer 3

The wave model.

Question 4

Give an example of a situation that can be described by either model?

Answer 4

Reflection.

Question 5

Describe Broglie’s initial theory.

Answer 5

• 1923, Louis de Broglie
• Suggested that all matter, regardless of its mass, could display wave-like properties.
• Evidence for this suggestion was provided by an experiment which showed that electrons showed wave-like behaviour, as well as behaving like particles.

Question 6

What do you have to do to prove that particles can also act as waves?

Answer 6

Show the particles exhibiting a wave-like characteristic/property, such as diffraction or interference.

Question 7

Describe the electron diffraction experiment.

Answer 7

Wavelength of electrons is much smaller than light.
Slit spacing of a diffraction grating is very large in comparison with an electron’s wavelength, so the spacing between atoms (similar to the electron’s wavelength) is used instead.

1) Electrons from an electron gun are accelerated through a vacuum towards a layer of polycrystalline graphite.
2) A polycrystalline material is made up of many tiny crystals, each consisting of a large number of regularly arranged atoms.
3) The electrons diffract as they emerge from the gaps between the atomic layers in the graphite film, and interfere constructively.

(Since the graphite atoms are not all lined up in the same direction as in a diffraction grating, this gives a circular pattern instead of parallel lines seen when light diffracts).

4) The image seen on the fluorescent screen is created when electrons striking the screen cause light to be emitted.

Question 8

What does electron diffraction provide evidence for?

Answer 8

The wave-like behaviour of particles.