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Presentation on theme: "REFRACTION."— Presentation transcript:


2 When light travels from one material to another it usually changes direction
The bending of light that occurs at the borderline of two materials is called refraction Geometrical concepts: -incident ray -refracted ray -normal to the point of incidence -incident angle -refracted angle

3 Refraction at the air-glass boundary

4 What happens during refraction?

5 This causes the light to bend or refract.
Why is light refracted? The speed of light depends on the material through which the light is travelling. When light enters a different material (e.g. from air into glass), the speed of light changes. This causes the light to bend or refract. glass air The speed of light is affected by the density of the material through which it is travelling. When light enters a more dense medium (from air into glass), its speed decreases and this is why refraction occurs

6 Refraction Frequency stays the same
Because the frequency of the wave is determined by the source, if the wave speed slows down, its wavelength must decrease. (And vice versa) Fast Medium - low refractive index like air Slow Medium - higher refractive index like glass Frequency stays the same

7 Willebrord Snellius (1580-1626)
Dutch astronomer and mathematician Most famous for the law of refraction (Snell’s Law) Found a new method for calculating the radius of the earth as well as π

8 The laws of refraction: Snell’s laws
If light travels from material 1 with index of refraction n1 to material 2 with index of refraction n2 the following laws determine the direction of the refracted ray: The incident ray, the normal to the incidence point and the refracted ray are all in one plane

9 Absolute Refractive Index (n)
is a measure of how much the speed is slowed when entering a medium from a vacuum (or air) n = speed of light in a vacuum speed of light in a medium Values include: n alcohol = n diamond = 2.41 n glass = n water = 1.33 Which substance does light travel the fastest? Why will you never get a number less than 1?

10 Why does the sky appear blue?
The atmosphere is densest (thickest) at the bottom, near the Earth. It gradually thins out as you go higher and higher up. The blue colour of the sky is due to Rayleigh scattering. As light moves through the atmosphere, most of the longer wavelengths pass straight through. Little of the red, orange and yellow light is affected by the air.

11 ………..continued However, much of the shorter wavelength light is absorbed by the gas molecules. The absorbed blue light is then radiated in different directions. It gets scattered all around the sky.

12 Effects of refraction Refraction causes visual effects such as this ruler appearing to be bent. This happens because light from the part of the ruler in the water is refracted as it travels from the water into the air. How does refraction make this stone look closer to the surface of the water than it really is? Light rays from the stone are refracted as they leave the water. The brain assumes that these rays have travelled in straight lines and is fooled into forming an image where it thinks the light rays came from. image actual location

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