Physics - Chapter 17

17.1 §

• Light travels quickly in some materials and slow in others
• Speed of light through any material is slower than it’s speed in a vaccum
• Index of Refraction - the factor by which a material reduces the speed of light
• Definition of Index of Refraction, n
  • Speed of light in a material = speed of light in a vacuum / index of refraction of the material
  • v = $\frac{c}{n}$
• Index of refraction for common substances
  • 
• Refraction - A change in direction due to change in the speed of a wave
• Snell’s law
  • Index of refraction 1 x sine of angle 1 = index of refraction 2 x sine of angle 2
  • n${}_1$sin${\theta }_1$ = n${}_2$sin${\theta }_2$
    • ${\theta }_1$ = angle of incidence
    • ${\theta }_2$ = angle of refraction
• Mirage - Optical illusion caused by refraction of light
• Refraction only occurs when light enters new material at an angle other than 90${}^{°}$
• Light is bent towards the normal when it slows down because it has entered a material with a higher index of refraction
• Light is bent away from the normal when it speeds up because it entered a material with a lower index of refraction
• If ray of light goes from one material to another along the normal it does not change direction
• Refraction causes objects to look bent
• Apparent Depth - when the object appears to be closer to water’s surface than it actually is
• Lifeguard textbook example, what path does lifeguard take to save someone drowning in the least time. Look at the path with highest distance on land where you can run fast and lowest in the water where you cant move as fast