I asked a student in class to walk out the door so that we do not see him, and speak to us. We heard him well, although we could not see him. How do we explain this?

 

Sound is waves in air, and diffracted (bent) through the door. Why did not light also diffract? The answer is that the wavelength of light is far smaller than the wavelength of sound. The wavelength of light is microscopic.

 

We have diffraction of light only for very small distances. For example, bring two fingers close to each other but not touching, and look through these fingers at the light. We will see what looks like a finger between them. This is diffraction.