Chapter 29 Reflection and Refraction. Reflection - when a wave reaches a boundary between two media,...

Chapter 29Reflection and Refraction

Reflection - when a wave reaches a boundary between two media, some or all of the wave bounces back into the first medium

Angle of indicence – the angle made between the incident light ray and the normal

Angle of Reflection – The angle made between the reflected ray and the normal

Law of Reflection: angle of incidence = angle of reflection

Reflection of an image on a flat mirror:

Candle appears as if it is behind the mirror

Virtual image – rays of light appear to originate from a point located behind the mirror. The image is called a virtual image, because light does not actually start there.

Diffuse Reflection – rays of light are scattered when reflected from a rough surface

• An echo is reflected sound

• All surfaces reflect sound (walls, ceilings, floor, furniture, people)

• When the walls of a room, auditorium, or concert hall are too reflective, the sound becomes garbled. This is due to multiple reflections called reverberations

• The walls of a concert hall are often designed with grooves so that the sound waves are diffused

Refraction:

• Waves bend when one part of each wave is made to travel slower (or faster) than another part

• Refraction is the bending of a wave due to a change in the wave speed as it passed from one medium into another

Refraction of sound over a lake:

Index of refraction – the ratio of the speed of light in a vacuum to the speed of light in a given material is called the index of refraction (n)

Index of refaction (n) = speed of light in vacuum speed of light in material

Snell’s Law(The Law of Refraction)

n sinθ = n’ sinθ’

Mirage – A mirage is formed due to the change in the speed of light in air of different density.

Hot air = less dense

Cold air = more dense

Dispersion – occurs when light composed of different wavelengths passes through a prism which causes separation of the light into its component colors

Critical Angle – A light beam that is incident upon the interface between two media is totally reflected at angles greater than the critical angle.

θ

Sin Θc = n2 Θc water: sin Θc = __1__ n1 1.33

sin Θc = .752

Θc = 48.8 degrees