Reflection vs. Refraction When light strikes a mirror, it is reflected. The law of reflection tells us that the reflected angle is equal to the incident angle.

Reflection vs. Refraction When light strikes the interface between two transparent materials, the light divides into two parts. Some is reflected (θ r = θ i ) The rest is transmitted across the interface.

Reflection vs. Refraction When a light ray enters the second material, it changes direction – it is refracted. The transmitted ray has a different direction than the incident ray.

Index of Refraction Light travels through a vacuum at a speed of c = 3.00 x 10 8 m/s As light travels through other materials (air, water, glass, etc.) atoms in the material absorb, reemit, and scatter the light. This results in light traveling through the material at a speed less than c.

Index of Refraction

Example 1

Snell’s Law of Refraction Light going from smaller n to larger n, ray is bent towards the normal. Light going from larger n to smaller n, ray is bent away from the normal. Angle of incidence Angle of refraction

Example 2 A light ray strikes an air/water surface at an angle of 46° w/r/t the normal. The refractive index for water is Find the angle of refraction when the direction of the ray is (a) from air to water and (b) from water to air. A) n1 = 1.00 (incident ray is in the air) θ1 = 46 ° n2 = 1.33 (refractive index of water) θ2 = ?

Example 2 part A n 1 = 1.00 (incident ray is in the air) θ 1 = 46 ° n 2 = 1.33 (refractive index of water) θ 2 = ? Air Water 46° Ɵ2Ɵ2 n 1 sinƟ 1 = n 2 sinƟ 2 Ɵ 2 =33°

Example 2 part A n 1 = 1.33 (incident ray is in the water) θ 1 = 46 ° n 2 = 1.00 (refractive index of air) θ 2 = ? Water Air 46° Ɵ2Ɵ2 n 1 sinƟ 1 = n 2 sinƟ 2 Ɵ 2 =74°

Mini-lab: Pencil in water Fill the beaker halfway with water Hold the pencil vertically in the center of the beaker View the pencil from the side with the beaker at eye level Slowly move the pencil towards the side of the beaker.

Mini-lab: Pencil in water Fill the beaker halfway with water Hold the pencil vertically in the center of the beaker View the pencil from the side with the beaker at eye level Slowly move the pencil towards the side of the beaker.

Apparent Depth An object lying under water appears to be closer to the surface than it actually is because light is refracted away from the normal when it enter the air. The eye sees the virtual image at the point where the refracted rays are extended back into the water (dashed lines)

Apparent Depth Example A searchlight on a yacht is being used at night to illuminate a sunken chest. At what angle of incidence Ɵ 1 should the light be aimed?

Example 2

Displacement of light by a transparent slab When light strikes a transparent slab with parallel surfaces, the emergent ray is parallel to the incident ray, just displaced from it. Apply Snell’s Law at each interface to prove it !

Assignment Focus p. 834 #1, 5 Problems p. 835 #1-3, 9, 10, 12, 16