Optics

Refraction

Optical Density

• Is a property of a material that is an inverse measure of the speed of light through the material.
• Different materials have different "speed limits"
• When light travels into a more optically dense material, it slows down.

Refraction

• Is the apparent bending of waves as they change speed at the boundaries of different materials.
• The angle between the refracted ray and the normal at the point of refraction is called the angle of refraction.

Reflection & Refraction

• At the boundary between two media, some of the light is reflected and some of the light is transmitted into the material and refracted.

Index of refraction

• Is a ratio of the speed of light in a vacuum to the speed of light in the material.
• n=c/v
• Is always greater than 1.
• Lets us calculate how much the light slows down.
• The slowing of the wavefronts (crests) causes the ray to appear to bend.

Snell’s Law

• Allows us to calculate how much the light ray will bend in a given medium.
• N₁sinq ₁= N₂sinq ₂

Critical Angle

• When a light ray moves into a less dense medium, it is possible to reach an angle where light cannot refract and escape, since sin q cannot be greater than 1!
• This is known as Total Internal Reflection.
• The Critical angle is the incident angle, such that the refracted angle is 90 degrees.

Lab Investigation

• Next Class you will complete a lab to measure the index of refraction for glass and water.

Check your Understanding