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