P1. You are in a boat spear fishing, aiming at fish underwater and to the side. You should aim ______ a) high b) low c) at the fish’s image.

P1. You are in a boat spear fishing, aiming at fish underwater and to the side. You should aim ______ a) high b) low c) at the fish’s image.

P2. You are in a boat fighting aliens that are underwater outside the boat. You use a powerful visible light laser gun. You should aim ______ a) high b) low c) at the alien’s image.

P2. You are in a boat fighting aliens that are underwater outside the boat. You use a powerful visible light laser gun. You should aim ______ a) high b) low c) at the alien’s image.

Dispersion Index n depends slightly on l,f (color) P3. Which has the highest index of refraction? a) red b) violet

Rainbows

Rainbows You see only the drops that refract/reflect visible light to you. Other drops refract light above and below you, forming rainbows you don’t see.

Converging (focusing, positive) lenses Thicker in the middle than on edges

Diverging (defocusing, negative) lenses Thinner in the middle than on edges

Imaging with thin lenses Same equations as for mirrors. Sign of f: +/-. Sign of di: + for real image side. - for virtual.

Imaging with a positive lens/mirror Dividing line: do>f or do<f Illustration

Imaging with a negative lens/mirror For any object distance, the image is ______, _______, and _______. upright----inverted real----virtual magnified---reduced

P3. A bug is 5 cm from a converging lens with f =10 cm P3. A bug is 5 cm from a converging lens with f =10 cm. The image is a) real, upright, magnified b) real, inverted, magnified c) virtual, upright, magnified d) virtual, inverted, magnified P4. The image distance is ____ cm. a) 2 b) 3 c) 4 d) 5 e) 10

Imaging with multiple lenses Use the image from the first lens as the “object” for the second lens. In this case we could have a negative (-) do…. …when the first “image” is beyond the 2nd lens

Space station astronaut and two balls of water

Total internal reflection

Total internal refraction (TIR) Occurs only going from ____ index to _____ index. Maximum q2 possible is 90o, and occurs when q1 is at the critical angle. For q1 > qc the ray is totally reflected. Illustration

Total internal reflection

Underwater view

P5. Which color will first be totally internally reflected if we start increasing the average n in the prism? red violet same

Why diamonds sparkle Very high index (n=2.4), so it’s easy to get light to totally internally reflect. Almost all the light comes back out the upper face or facets!

100% reflectors made only of glass, plastic “Corner cubes”: light goes back to the source!

Optical fibers and “light tubes” rely on total internal reflection Can transmit light signals for hundreds of km without much loss.

Imaging optical fiber bundles An ordered array of thousands of fibers…very expensive. Each fiber is a pixel. But cameras can be made small to replace these.

Mirages

Air index is lowest near the hot ground Imagine the air made of many layers of different n. Ray turns away from normal. At some point it is totally internally reflected, then turns toward normal