Refraction

Definition: Refraction Refraction is the movement of light from one medium into another medium. – Refraction causes a change in speed of light as it moves from one medium to another. – Refraction can cause bending of the light at the interface between media.

To describe how much the speed of light is affected by going from one medium to another, we use index of refraction

Index of Refraction

Refraction of light simulation htRefract.html htRefract.html

What happens when light hits the boundary between two transparent mediums? 1)Part of the light is reflected – usually less than 5% 2)The rest is transmitted across the boundary -The transmitted ray has a different direction than the incident ray – it is refracted (bent at the boundary) -If the transmitted ray travels from a medium with a higher (n) value to a medium with a lower (n) value the refracted ray will bend away from the normal -If the transmitted ray travels from a medium with a lower (n) value to a medium with a higher (n) value the refracted ray will bend towards the normal

n1 > n2 n1n1 n2n2 11 22 When the index of refraction decreases, light bends away from the normal. When n 1 > n 2  1 <  2

n1 < n2 When the index of refraction increases, light bends toward the normal. n1n1 n2n2 11 22 When n 1 < n 2  1 >  2

Snell’s Law n 1 sin 1 = n 2 sinϴ 2

Example: Snell’s Law A search light on a yacht is being used at night to illuminate a sunken chest. At what angle of incidence Θ 1 should the light be aimed?

Dispersion The separation of white light into colors due to different refractive indices for different wavelengths is called dispersion. Dispersion is often called the prism effect.

Dispersion Which color of light has the greatest refractive index?

Critical Angle

Remember – when light passes from a medium with a higher (n) to a lower (n), the light will bend away from the normal

This drawing reminds us that when light refracts from a medium with a larger n into one with a smaller n, it bends away from the normal. n1n1 n2n2 n 1 > n 2

If the angle of incidence increases so does the angle of refraction - Critical angle is reached when the angle of refraction = 90 o

Critical Angle of Incidence Instead of refraction, total internal reflection occurs when the angle of incidence exceeds the critical angle. n1n1 n2n2 cc  r = 90 o n 1 > n 2 Ray reflects instead of refracting.

Calculating Critical Angle n 1 sin  1 = n 2 sin 2

Example: Critical Angle The drawing shows a ray of light whose angle of incidence is Θ 1 = 68.3 o, traveling through two solid materials and then undergoing total internal reflection at a solid-liquid interface. What is the largest possible index of refraction for the liquid?