Ever wonder how you can hear someone's conversations without being seen? It can be a um.. wonderful thing for some people. Eavesdropping makes use of the fact that sound can diffract or bend as it travels through walls, or doors. Light waves, however, cannot bend in this matter, this way you can hear sound from around the corner without being seen.
Sound is also measured in decibels, and the closer you are the more decibels you can get, which includes more physics. You can use physics to determine how close you should get for the minimum amount of decibels for a person can hear, but you might want to hear a few extra decibels to make sure you get every detail.