05 – Lateral Displacement & Deviation PW3 - Refraction 05 – Lateral Displacement & Deviation

Lateral Displacement When light passes from air into glass and back into air, the light refracts twice. If the two refracting surfaces are parallel, the emerging refracted ray is parallel to the incident ray, just shifted over to the side. This shift is called lateral displacement (L.D.).

Finding Lateral Displacement 1. Draw the incident ray straight through as if it did not refract. 2. Construct a normal at the incident side and measure angle i.

Finding Lateral Displacement 3. Use n1sinθ1 = n2sinθ2 to determine the angle of refraction. 4. Construct the angle of refraction and the refracted ray.

Finding Lateral Displacement 5. Construct normal #2 where the refracted ray meets the 2nd side. 6. The original incident angle will be the same as the angle made by the emerging ray back into the air (< i = <R2), 7. Construct the emerging angle (<R2), measured from normal #2 and draw the emerging refracted ray. 8. Measure the perpendicular distance between the emerging ray and the line where the incident ray would have traveled had it not refracted – this distance is the “lateral displacement”

Angle of Deviation When light passes from air into glass and back into air, if the refracting surfaces are not parallel (like a prism), then the emerging ray takes a different path than as it entered the glass. The angle between the different path of the emerging ray and the incident ray is called the angle of deviation.

Finding Angle of Deviation 1. Draw the ray straight through as if it had not refracted. 2. Construct a normal at the incident side and measure angle i.

Finding Angle of Deviation 3. Use n1sinθ1 = n2sinθ2 to determine the angle of refraction. 4. Construct the angle of refraction and the refracted ray. 5. Construct normal #2 where the refracted ray hits the opposite side of the triangle.

Finding Angle of Deviation 6. Measure the angle between normal #2 and the refracted ray in the triangle – this becomes the incident angle (i2) for the ray as it goes from the triangle into air. 7. Use n1sinθ1 = n2sinθ2 to determine the angle of refraction (<R2) as the ray passes into air. 8. Measure this angle and construct the emerging ray.

Finding Angle of Deviation 9. Project the emerging ray backwards until it meets the original incident ray had it not refracted (step 1). 10. Measure the angle of deviation from the emerging ray to the incident ray (had it not bent).

Dispersion Dispersion is when white light is split into component wavelengths after leaving a prism The angles of deviation between the wavelengths grow large enough that you can begin seeing separate colours

Rainbows Rainbows are caused by TIR and Dispersion working together

Double Rainbow!