sections 26-3 – 26-5 Physics 1161: Pre-Lecture 22 Reflection and Refraction of Light

Physics 1161: Lecture 17, Slide 2 Light Doesn’t Just Bounce It Also Refracts! Reflected: Bounces (Mirrors!) Refracted: Bends (Lenses!) ii rr 11 22 n2n2 n1n1  i =  r n 1 sin(  1 )= n 2 sin(  2 )

Speed of light in medium Index of refraction Speed of light in vacuum so Index of Refraction 186,000 mi/s (3 x 10 8 m/s): it’s not just a good idea, it’s the law! always!

Physics 1161: Lecture 17, Slide 4 Indices of Refraction

Snell’s Law When light travels from one medium to another the speed changes v=c/n, but the frequency is constant. So the light bends: n 1 sin(  1 )= n 2 sin(  2 )

n1n1 n2n2 Snell’s Law Practice normal A ray of light traveling through the air (n=1) is incident on water (n=1.33). Part of the beam is reflected at an angle  r = 60. The other part of the beam is refracted. What is  2 ? sin(60) = 1.33 sin(  2 )  2 = 40.6 degrees  1 =  r =  11 rr Usually, there is both reflection and refraction!

n2n2 n1n1 d d Apparent depth: Apparent Depth 50 actual fish apparent fish