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# Why is this refraction and not reflection?

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1. As far as I know the reason the wavelength decreases in shallow water in the first place is because part of the wave hits the ground, resulting in becoming more transversal. I guess this is due to reflection?

In the above scenario why is the water refracted and not reflected?
2. Refraction is where the angle is changed, in this case due to a change of speed because part of the wave is moving through deeper water and part of it through another shallow water. The two parts of the wave travel at a slightly different speed, causing a change in angle of the wave.

Reflection is where the wave bounces back. Not happening in this case.

(Edits in bold)
3. Oh, I guess you mean they are travelling through air due to water waves being slightly transversal, but that isn't unique to the shallow area is it? In that case isn't the water wave being refracted all the time?

The explanation seems to be implying the glass is the source of the refraction and I was under the impression the wave was coming into contact with the glass which is why I thought of reflection
4. (Original post by Bobby132)
Oh, I guess you mean they are travelling through air due to water waves being slightly transversal, but that isn't unique to the shallow area is it? In that case isn't the water wave being refracted all the time?

The explanation seems to be implying the glass is the source of the refraction and I was under the impression the wave was coming into contact with the glass which is why I thought of reflection
Firstly, my full apologies, in a rush I skimmed the equation and got the wrong idea. But the theory is the same.

What's happening in your example is that we are changing the depth of water (by placing an obstacle in the tank). The depth of the water changes the speed of the wave, and if one 'end' of the wave hits shallow water before the other, the wave will bend due to each section travelling at different speeds.

Are you happy with that?

If a wave was to hit the glass block it would be reflected, but as this is under water, this is not the behaviour that we are observing.

Feel free to challenge me if I've cocked up!
5. But is the reason the wave slows in the first place because it is coming into contact with what is under it (in this case the piece of glass)?

Would that mean first there is reflection and because of the reflection there is refraction?

What do you think of this explanation?

Waves through the water are oscillations in the displacement of the water molecules, up and down - it is not possible in any at all straight-forward way for such waves to propagate through into a solid medium like glass, as would have to occur for the waves to be refracted. Of course a solid like glass can support oscillations travelling through it, but at frequencies so very much higher than those you would create in a ripple tank (approx a million times) that on meeting the glass, the wave would essentially be entirely reflected.
6. (Original post by Bobby132)
But is the reason the wave slows in the first place because it is coming into contact with what is under it (in this case the piece of glass)?

Would that mean first there is reflection and because of the reflection there is refraction?

What do you think of this explanation?
No because the waves are not refracting through the glass, they are refracting in the shallow water that runs over it.

All you are observing is the surface waves; these waves are refracting, not reflecting. Remember that these waves on top will act independently of those underneath. Underneath there will be reflection of waves (essentially) but this is not visible to you and does not affect the refraction of the surface waves, which you are observing.

The explanation you posted helps us to understand that if the glass block was too high for water to pass over (taller than the water is deep) then the waves would not be refracted, but only reflected. It would completely block the path, and the water waves are not able to pass through it. So they are reflected.

In your example (OP) the water waves CAN pass over the glass block, so they do, but because the water here is shallower, the waves have less speed, and because part of the wave reaches shallow water before the rest, this speed difference causes bending.

So, essentially, yes the glass block would cause reflection, but you are not concerned with these waves (under the surface, which are not visible) only with those on top, which refract due to the change in speed caused by the change in depth of the water; NOT due to reflection underneath the surface.

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