For light, wave-particle duality works like this. To understand some aspects of how light behaves, such as interference and diffraction, you treat light as a wave. To explain other aspects (photoelectric effect and Compton effect) you treat light as being made up of particles. Light exhibits wave-particle duality, because sometimes it acts like a wave and sometimes it acts as if it is made up of particles.

Things we usually think of as particles exhibit wave-particle duality too. The behavior of relatively large objects, like baseballs, is dominated by their particle nature; to explain the behavior of very small things like electrons, however, both wave properties and particle properties have to be considered.

Examples of particles showing wave properties:

• Electrons passing through a double slit set up an interference pattern on a screen much like the pattern we obtained with light.
  
  
• High-resolution images can be obtained with electron microscopes. In a microscope the size of the smallest features we can see is limited by the wavelength used. With visible light the smallest wavelength is 400 nm. Typical electron microscopes use wavelengths about 1000 times smaller, and can therefore be used to study very fine details.
  
  
• Light waves (usually x-rays) are used to study crystal structure via diffraction. Similar diffraction experiments have been done with electrons, neutrons, and atoms of hydrogen and helium.