Reflection and Refraction

• Visible light is part of the electromagnetic spectrum and is a transverse wave
• Light waves are transverse: particles vibrate perpendicular to the energy transfer
• Light can undergo reflection and refraction
• Sound waves are vibrations of air molecules
• Sound waves are longitudinal: particles vibrate parallel to the energy transfer
• Sound waves can cause a drinking glass to vibrate and shatter
• Sound can undergo reflection and refraction
• Reflection occurs when a wave hits a boundary and stays in the original medium
• An identical image of an object can be seen in water due to reflection
• Refraction occurs when a wave passes a boundary between two different transparent media and changes direction
• Waves can change direction when moving between materials with different densities
• The Law of Reflection states that the angle of incidence is equal to the angle of reflection
• Refraction occurs when light passes a boundary between two different transparent media and undergoes a change in direction
• Light bends towards the normal when going from less dense to more dense media
• Light bends away from the normal when going from more dense to less dense media
• When light refracts, it does not change color
• Snell's Law: when light enters a denser medium, it slows down and bends towards the normal
• The amount of bending depends on the density of the material
• If light travels from less dense to more dense medium, it bends towards the normal
• If light travels from more dense to less dense medium, it bends away from the normal
• Snell's Law equation: n = sin(i) / sin(r)
• Refractive index is a number related to the speed of light in a material, always less than the speed of light in a vacuum
• Refractive index is always larger than 1 and different for different materials
• Objects more optically dense have a higher refractive index, e.g., n is about 2.4 for diamond
• Objects less optically dense have a lower refractive index, e.g., n is about 1.5 for glass
• Refractive index is a ratio and has no units
• Snell's Law: n = refractive index of the material, i = angle of incidence of light (°), r = angle of refraction of light (°)
• Total Internal Reflection (TIR) occurs when the angle of incidence is greater than the critical angle and the incident material is denser than the second material
• Two conditions for TIR: Angle of incidence > critical angle, incident material denser than second material
• Total Internal Reflection is utilized in optical fibers (e.g., endoscopes) and prisms (e.g., periscopes)
• Critical angle is the angle at which light is refracted along the boundary, leading to TIR when angle of incidence is larger than critical angle
• Critical angle is related to refractive index by the equation: sin(c) = 1/n
• Larger refractive index of a material, smaller the critical angle, more likely for TIR to occur
• Comparison of critical angles: Opal (n = 1.5) has a critical angle of 42°, Diamond (n = 2.4) has a critical angle of 25°
• Diamond will appear to sparkle more than opal due to a lower critical angle allowing for more TIR