Light

Light – Wave or particle? For many years scientists argued over the nature of light, "Is light a wave or a stream of particles?" In some experiments light exhibits wave like properties, the Doppler effect, interference, refraction, diffraction and in other experiments, like the photo electric effect, it exhibits particle like properties The fact is that light exhibits behaviors which are characteristic of both waves and particles.

Early Concepts of Light Early Greek philosophers: tiny particles entering the eye to create vision Socrates & Plato: streamers/filaments from the eye contacting the object. “How else can you explain why you don’t see an object until you look at it?” Newton: light made of particles

The Speed of Light Does light take time to travel, or does it arrive at the same instant it departed? Ancients: speed of light is infinite 1880: Michelson measured speed to be about 300,000 km/s

Electromagnetic Waves Visible light is a small part of the electromagnetic spectrum EM waves with higher frequency than visible light are ultraviolet EM waves with lower frequency than visible light are infrared

Light and Transparent Materials LIGHT 3 of many atoms LIGHT GULP! BURP! GLASS a b c d e f g Chain of absorptions/re-emissions

Opaque Materials Reflect light instead of transmitting Opacity in one part of the EM spectrum, transparent in another part – EX: People are opaque in visible light, more transparent in X-rays Also called M31, this is closest neighboring galaxy in the wider universe and is just about visible from a good site. Radio, microwave, infrared, visible, ultraviolet and x-ray.

Opaque Materials Can only reflect a color if that color is present in the incident light Shadows:

RGB Color Mixing

Polarization

BUT... There’s a controversy! “DST” – Dark Sucker Theory Electric bulbs = “Dark Suckers” Candles are primitive DSs Portable DSs need a Dark Storage Unit Dark has mass Dark is heavier than light Dark is faster than light

BUT... There’s a controversy! Finally, we must prove that dark is faster than light. If you were to stand in a lit room in front of a closed, dark closet, and slowly opened the closet door, you would see the light slowly enter the closet. But since dark is so fast, you would not be able to see the dark leave the closet. Next time you see an electric bulb, remember that it is a Dark Sucker.

The Color Spectrum Homework for next time: Read Chapter 27, Hewitt: Do RQ 1-23, T&E1,4- 10 Chapter 28 – Will pull extra credit questions from here!