Light!

General Properties of Light Isaac Newton: believed light was a series of fast moving small particles Now we know: light behaves both as particles (quanta) and waves (electromagnetic waves) Ray model of light: path of light drawn as a straight ray

Light Speed! Galileo hypothesized that light has a finite speed Ole Rømer: worked for Cassini, observed Jupiter's moons in 1677 Observed that times between eclipses got shorter as Earth travelled toward Jupiter Hypothesized that light took less time to reach Earth when Earth moving toward Jupiter Calculated speed of light as 2.2 x 10 8 m/s

Light Speed! Albert A. Michelson measured time for light to travel between mountains 35 km apart in 1883 Calculated speed to be x 10 8 m/s

Light Speed Speed of light in vacuum is a constant ( C ) C = x 10 8 m/s One light year is the distance light travels in one year 1 ly = 9.46 x km

Electromagnetic Spectrum EM Spectrum: classification of frequencies of all waves that travel at speed of light Light commonly described by wavelength or by frequency

Electromagnetic spectrum Radio waves: 3Hz- 300 MHz ( km - 1m) used for communication Microwaves: 300MHz-300GHz (1m-1mm) used for communication and microwave ovens

Electromagnetic spectrum Infrared (1mm – 700 nm) heat, communication Visible light (700 nm – 400 nm) Ultraviolet (400 nm – 10 nm) used to sanitize, forensics, vitamin D

Electromagnetic spectrum X rays (10 nm – 0.01 nm) used to detect fractures/flaws Gamma rays (0.01 nm and less) may be used to sterilize