Homework Set 3 From “Seeing the Light” Chapter 2: (starting page 68) P22, P24, P26, PM4, From “Seeing the Light” Chapter 3: (starting page 101) P1, P2, P3, P4 Due: Monday, Feb 23

Dispersion of light What is dispersion? And how it comes about? Optical Properties of diamonds –Brilliance, fire, and flashes Rainbow –how does it happen? –Why everyone sees a different rainbow?

Newton’s Discovery Newton (at the age of 23) reached the revolutionary conclusion that white light is not a simple, homogenous entity, as natural philosophers since Aristotle had believed. When he passed a thin beam of sunlight through a glass prism, he noted the oblong spectrum of colors: red, yellow, green, blue,violet– that formed on the wall opposite.

Dispersion The index of refraction is not a constant! It depends on the frequency of the light! This is because the light with different frequencies wiggles the charges with a different speed. Examples: water glass diamond Red =656 nm Yellow =589 nm Blue =434 nm

THE SECRET Different frequencies of the light bend different amount as it passes through a dispersive media.

Optical properties of diamonds Why are the diamonds expensive? brilliance!Diamonds has a large index of refraction (n=2.4) and has a small critical angle 24.5°. The diamond surfaces are cut so that most of light entering a diamond is eventually reflected back out the front  brilliance! – if you look from the back, the diamond is black.

the fire of diamonds: beautiful colorsDiamond is highly dispersive. So the white light is spread out into a broad spectrum  the fire of diamonds: beautiful colors.

Flashes Diamonds are cut with many surfaces. When viewed from one angle, some light gets reflected from a particular surface and its color spreads out, reaching your eyes. flash (sparkleAs you turn the diamonds or yourself, some other rays reach your eyes with other paths. And this causes the flash (sparkle) of the diamonds.

Rainbows Because of the dispersion of water, droplets of water can break up the sun light into a spectrum  rainbow How does this happen, precisely? –A light beam is dispersed twice through raindrops and reflected once….

42°

Since the red rays bend less than the blue, they have a steeper opening angle relative to the horizontal. you see the red rays from all those raindrops that lie at 42° relative to the horizontal sun rays –A math calculation shows that you see the red rays from all those raindrops that lie at 42° relative to the horizontal sun rays. The blue rays bend more, and have smaller opening angle relative to the horizontal. –You see the blue rays from all those raindrops the lie at 40°.

Thus all rays from a rainbow come from different raindrops. And everybody sees a different rainbow!