# Light ray problem

#### 7bear

1. If a light ray go through a boundary of air and glass(i.e. angle of incidence is 90 degree), Is there any refraction or reflection?
2. If angle of incidence is 0 degree( the light ray is normal to a glass), Is there any reflection?
3. Suppose the situation is same as (2), but the light ray go from air to water. Is there any refraction or reflection?

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#### kuenmao

1. Light can either go through the air next to the glass, or the glass next to the air. There's no such thing as a boundary that can be travelled through. So I guess if you do it very accruately, the answer depends on where you enter the glass from air.
2. Yes. A very weak one. You don't see it, however, because it coincides with light beam that is travelling towards the glass block.
3. Whenever something is going normal to the surface, then it won't have any refraction. Refraction occurs only when the incident ray is at an angle to the surface. However, there will be a (weak, very weak) refracted ray.

1. Yes, there is refration and reflection. If you look at a piece of blass in front of you, you will see the stuff behind it and you will also see a faint mirror image of yourself. This is called partial reflection, and it has a LOT to to with quantum physics. It wanges anywhere from 4% to 16%. But this is a long stody.
2. Look at my answer to number 1.
3. Water, I am not shure of. Im not shure if the same phenomenon happens as in glass, but by experience, it seems to me that there is both.

#### Claude Bile

1. Yes, there is still reflection. There is no refraction in the sense that the light ray does not bend, however it is still generally referred to as a refracted ray.

2. The Fresnel reflections from an air glass interface is about 4%. Antireflection coatings on the surface of the glass can reduce this to well below 0.01%.

3. Yes, anywhere where the refractive index changes abruptly, there will be significant reflection and refraction effects.

Claude.

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