# Reflection, refraction, diffraction, wave superposition

Explain the behaviour of waves in a variety of situations by investigating the phenomena of:
– reflection

refraction
– diffraction
– wave superposition

Learn.

Mechanical waves are the net movement of energy, not the medium itself – it is important to remember this.

When two waves move through the same medium and overlap, they interfere with one another, this can be seen in a skipping rope if people make a pulse which travels along it, the area of overlap will result in interference. The waves will then continue along the rope. This phenomena of interference is known as superposition. The regions where the pulse is a peak and a peak will add together and the peaks and troughs will cancel one another out. When the waves add together it is known as constructive interference and where they cancel one another it is known as deconstructive interference.

Reflection creates the echo effect. After all, sound is a mechanical wave. If you go to a large area and yell, the sound will bounce off the neighboring mountains and you will here your voice. This can also be seen in the skipping rope when you create a pulse, it will rebound off the other side and return back to you.

Refraction occurs when a wave changes mediums. This causes the wave to change direction slightly veering one way when it changes mediums of varying density. For example the light bends to the left when it goes from low density air to high density plastic in the below picture. The when leaving the high density plastic and returning to low density air it bends back. This can be defined by snell’s law and we will go into more depth later on.

Have you ever been sitting in another room and heard people speaking? This every day phenomena is known as refraction . It occurs when a mechanical wave bends around a medium. When you heard the sound in the opposite room, you were not in direct line of sight, rather the sound had to bend around an obstacle to reach you. The shorter the wavelength of the light the greater amount of refraction – this is why you can usually hear higher noises if someone leaves there window open and you are behind the car.

Memorize.

Reflection :

Refraction:

Diffraction:

Wave superposition:

Master.

Question 1.

Compare and contrast constructive and deconstruction interference. [2 marks]

Question 3.

Define, providing an example: [2 marks each]

• Reflection
• Refraction
• Superposition
• Diffraction

Extension

Question 2.

A wave is heading towards an object it rebounds off it and bends around it. Explain what phenomena you would expect to observe. [5 marks]

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