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# Physics - refraction Watch

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1. A three year old was heard to remark at a barbeque (bbq) "The trees look like jelly - they're all wobbly"
She was looking at the trees over the top of the bbq. Heated, less dense air was rising from the bbq in unveven layers chaning the direction of the light from the trees in a varying pattern.

Q1)
The tree trunks appeared like thus before the bbq hot air
A------B--------C
The tree trunk B was directly opposite the viewing site of the child (i.e: straight ahead) and A and C were at slight peripheral angles.
After the bbq was lit A and C appeared closer to B while B remained unchanged..
Explain this.

Q2)
Explain why the trees appeared all wobbly
2. Light will travel at a slightly faster speed in the heated, less dense air.
What happens then as a result when light moves from a dense to a less dense medium? (Think of water or glass as the more dense medium and air as the less dense; and what happens then.)
3. (Original post by Stonebridge)
Light will travel at a slightly faster speed in the heated, less dense air.
What happens then as a result when light moves from a dense to a less dense medium? (Think of water or glass as the more dense medium and air as the less dense; and what happens then.)
The light will bend away from the normal.

Oh, so A and C will appear closer because light bends towards B as it moves faster through the less dense region.

as to why they appear wobbly, I don't know. Might it have to do with the fact the the hot layers of air mix with cooler layers of air constantly?
4. right?
5. (Original post by jsmith6131)
The light will bend away from the normal.

Oh, so A and C will appear closer because light bends towards B as it moves faster through the less dense region.

as to why they appear wobbly, I don't know. Might it have to do with the fact the the hot layers of air mix with cooler layers of air constantly?

(Original post by jsmith6131)
right?
Yes. The light will refract away from the normal. This will make A and C appear closer.
A simple ray diagram would show this more clearly.
Yes. The warm air rising will be unstable in the sense that it will billow and swirl; so the amount of refraction will not stay constant.
6. Is this for AS?

I don't remember any questions like this from AS based on refraction, all we really had to know was the definition.

But yeah the trees could we wobbling because the light is changing direction when passing through the heated air.
7. yes it is
8. What board?

I did OCR, and I'm resitting the exam in Jan and I've never seen a question like that in any past papers.

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Updated: December 28, 2010
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