# Refraction of light! help (1 Viewer)

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#### md6616

i need an explanation for this situation.
i've inserted an pingpong ball into a glass full with water (the glass is made out of thick glass if it matters somehow?).
Now what happened is that the half of the ball that is in the water looks much bigger than the half that is not in the water.

My question is why the ball that is in the water looks so big? how does it connected to light refraction?

p.s- I added a sketch for you to understand better the situation!

A reply would be very much appreciated

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#### Claude Bile

The cylindrical shape of the glass+water acts as a lens, magnifying the ball. Lenses cause this magnification because of the way light refracts.

Claude.

#### md6616

!

Would you mind adding a more detailed explanation or to direct me to website that will explain it more clearer?

#### ranger

##### King of all llamas
Gold Member
Since the water surface is not flat - becuase of the container and other factors. The light is bent into a new path. The light is bent outwards and is spread out.

http://en.wikipedia.org/wiki/Refraction

#### md6616

Since the water surface is not flat - becuase of the container and other factors. The light is bent into a new path. The light is bent outwards and is spread out.

QUOTE]

Why does the water surface isn't flat?
and what do you mean by "The light is bent outwards"? outwards from where?
and how it causes the ball to look magnified? ( is it because the combination of water and glass acts like a magnifying lens like Claude said?)

#### ranger

##### King of all llamas
Gold Member
Since the water surface is not flat - becuase of the container and other factors. The light is bent into a new path. The light is bent outwards and is spread out.

QUOTE]

Why does the water surface isn't flat?
and what do you mean by "The light is bent outwards"? outwards from where?
and how it causes the ball to look magnified? ( is it because the combination of water and glass acts like a magnifying lens like Claude said?)
In order to understand how an immersed object is magnified, I guess an understanding on how a typical magnifying glass magnifies an object would be a good start. They make use of the principle that light changes velocity as it travels in mediums of different densities. As light moves from air to a more dense medium, lets say water, the light in refracted (bent) [towards the normal]. The larger the change in the index of refraction, the more the magnification.

Now imagine that you and the ball are both immersed in water. Do you think there would be magnification? Why [or why now]? To complicate the situation, what if you had a magnifying glass with you under water?

So what you said is correct - it does act like a kind of lens.

Thanks ranger :)

#### md6616

one more question!
Does the combination of water and cylinder shaped glass creats the effect of cylindrical lens?

#### 3trQN

Anyone want to attempt a QED explanation?

#### Claude Bile

one more question!
Does the combination of water and cylinder shaped glass creats the effect of cylindrical lens?
Yes, you'll notice that the ball is magnified along the horizontal axis but not the vertical.

Claude.

illustration

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#### linux kid

hmm...if light rays are basically refracted further apart, then why don't we get a certain distortion (blind spots)?

#### cesiumfrog

just curious
In this domain, the ray approximation of light is sufficient to understand the image (combined with snell's law of refraction).

If you wanted, you could try to understand snell's law of refraction. You could do so by switching to wave (rather than ray) optics (combined with knowledge of the wave velocity in various media).

If you wanted to understand why wave optics is relevent (and why the wave velocities differ among media), you might study classical electrodynamics. In depth. I'm just saying it would be a long time before you understood the physics of your problem well enough to be able (or to need) to use quantum electrodynamics to further improve your understanding.

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