Light … is an electromagnetic wave: … is a wave pattern of electric and magnetic fields … propagates in vacuum … has wavelength (blue: 400 nm, red: 700 nm) The physics of light 1 mm = millimeter 1000  m = 1 mm 1000 nm = 1  m Micrometer (size of a germ) Nanometer (size of ten atoms) Learn units of distance! 0.4  m0.7  m Millimeter (size of ant)

Olaf R ömer Speed of light c = 300,000 km/s: Discovered by: Olaus Roemer (1675) Eclipses of Jupiter ’ s moons come a few minutes late when Jupiter is on the far side of its orbit. Reason: light needs extra time to reach us. Conclusion: light needs 9 minutes to traverse the Sun-Earth distance. Watch 07JupiterMoonDance.mov Light takes a few minutes/hours to move around in the solar system years or more to go from star to star

The electromagnetic spectrum Light has a wavelength: Wavelength of light means color: Blue has short wavelength Red has long wavelength What is beyond blue? Bluer than blue is UV (ultraviolet) - even shorter wavelength Redder than red is IR (infrared) - even longer wavelength These are colors of light invisible to the eye.

The full spectrum And what is beyond those wavelengths? (A prism breaks up white light into colors.) They all move with the same speed c = 300,000 km/s Radio | Infrared | Visible | Ultraviolet X-ray|  -ray Need spacecraft (Far UV, X-ray,  -ray) Need spacecraft Eye / Telescope Radio antenna Prism Slit White light

Questions coming …

sec 30 Question Which one is moving fastest? A Radio waves B X-rays C Visible light D Laser E The same Next question coming …

sec 30 Question What is the difference between red and blue light? A Intensity. B Speed. C Wavelength. D Blue is composite, red is not. E Red is existence of light, blue is lack of light Next question coming …

sec 45 Question Next question coming … How many of the following types of “ light ” penetrates the atmosphere? Radio waves Far IR Regular light Far UV X-rays A 1 B 2 C 3 D 4 E 5

sec 30 Question How was the speed of light measured for the first time? A In an experiment with a laser beam. B By the time delay the astronauts ’ answer came from the Moon. C Observing the moons of Jupiter. D By measuring the radar signal reflected by the Moon. E By measuring the time light takes to arrive to us from another galaxy

Structure of atom Recall:  Chemistry cannot change the nucleus, only bind atoms into molecules  Isotopes: same number of p and e, different n. Same chemical properties. Examples: H: 1 p0 n1 e Deutron:1 p1 n1 e (same as H but heavier) He:2 p 2 n2 e

Turn in your scantron now personally!