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Refraction of Light
What is Refraction?
Refraction is the bending of a ray of light when it goes from one medium to another.
Light usually travels in a straight line but when it changes medium it may change direction and this is called refraction. However if the ray hits the object straight on there is no refraction. Refraction only occurs at an angle (As shown in diagram).
- The ray of light falling on the box is called the incident ray
- The line drawn at right angles to the box where the ray strikes the box is the normal at the point of incidence.
- The ray of light in the box is the refracted ray.
- The angle between the incident ray and the normal is called the angle of incidence (i).
- The angle between the refracted ray and the normal is called the angle of refraction (r).
When light travels from a rarer medium to a denser medium the ray is refracted like in the diagram. However if it travels from a dense to a rarer medium it is refracted away from the normal.
Example of Refraction
When a spoon or pencil dips into a dish of water it appears to bend when it enters the water. This is a clear example and effect of refraction.
Laws of Refraction
There is an exact relationship between the angle of incidence and the angle of refraction.
- The incident ray, the normal and the refracted ray all lie on the same plane.
- The ration of the sine of the angle of incidence to the sine of the angle or refraction is a constant.
Sin i / Sin r = n (which n is a constant) - (This is Snell's Law)
Real Depth / Apparent Depth = n
Speed of light in medium 1 / Speed of light in medium 2 = n
Refractive Index is "n" in the above equations. It tells us how well something slows down light. Some examples are:
Air: 1 (1.0003)
Water: 1.33 = 4/3
Glass: 1.5 = 3/2
Diamond: 2.4 = 12/5
Refractive Index is a ratio and therefor has no units.
Real Depth Vs. Apparent Depth
Because of refraction, when you look into a swimming pool the pool floor looks closer than it actually is. This gives us an apparent depth and a real depth. We can also find the refractive index this way.
n = Real Depth/ Apparent Depth