# Reflection versus Refraction with Waves

I am a middle school science teacher and we teach a unit on waves (mostly about sound) My students struggle to identify whether a wave (usually sound) is refracting or reflecting across many different situations. At a middle school level would it be reasonably accurate for them to think about reflection as any situation where the sound wave must return to the source? (Echoes, SONAR, color of objects, mirrors).

The only examples we've encountered that do not follow this general rule are seismic waves reflecting off different layers inside the Earth and sounds that pass through the diaphragm of a stethoscope. (We do not go into much detail about seismic wave behavior beyond absorbing)

• I do not think this is reasonable even "At a middle school level" .... "to think about reflection as any situation where the sound wave must return to the source?" because if you tilt the mirror (not perpendicular to the ray) then the reflected ray does to return to the source, see upload.wikimedia.org/wikipedia/commons/1/10/… Jan 29, 2023 at 14:48

Suppose you have two media that meet at an interface. Sound starts in medium 1 and hits the interface.

The wave is reflected off the interface if it stays on the same side and stays in medium 1.

The wave is transmitted if it crosses the interface and enters medium 2. Typically the wave changes speed and direction as it crosses because the two media have different properties. Refraction refers to the change in direction as the wave crosses the interface.

Often part of a wave will be reflected and part transmitted/refracted.

If you are talking about seismic waves, you may be talking about a non-uniform medium, where the properties change continuously from one part to another.

In this case, you can see refraction as the wave passes from one part of the medium to another. Instead of an abrupt change in direction at a boundary, the wave may follow a curved path in a single medium.

In all cases, refraction is a change in wave speed and direction caused by changes in the properties of the medium in which it travels.

• Ah thank you! I see now how to explain this to students so they can always tell the difference between reflection and refraction. If the wave moves from one medium to another, the wave will refract. (I know this is a generalization and the truth is much more complicated). Situations we've given them include sonar, colors of objects, echoes, and sound waves traveling where there are temperature differences (air and water). The last one is definitely the hardest for them, but knowing temperature effectively makes it two different mediums, they can link that fact to refraction. Thanks!!
– npez
Jan 29, 2023 at 1:11
• @npez if this is the right answer to your question could you please go ahead and mark it as "the answer"? This is both to attribute the correct answer to the person who answered it but also (equally or possibly even more important) for future reference to people who may have the same question as you. Jan 29, 2023 at 12:04