Light Physics Mrs. Coyle

Light is a wave Light shows properties of waves: Diffraction patterns observed

Light is a Particle Light can travel through the vacuum of space, but mechanical waves can’t travel in a vacuum.

So which is it?

Electromagnetic Waves: oscillating electric and magnetic fields.

Electromagnetic Waves Do not require a medium. Can travel through space (vacuum). Ex.: Light from the sun reaches us. Transverse

Electromagnetic Waves Type of radiation Wavelengths(m) Radio 570 - 2.8 TV 5.6 - 0.34 Microwave 0.1 - 0.001 Infrared radiation 10-3 - 10-7 Visible Light 700x10-9 - 400x10-9 Ultraviolet 10-7 - 10-10 X-rays 10-10 -10-12 Gamma rays shorter than 10-12

Visible Light is detected by the human eye. red 700 x 10-9 (700nm) orange yellow green 550 x 10-9 blue indigo violet 400 x 10-9 (400nm)

Electromagnetic Spectrum

Speed of Light, c All EM waves have a speed through vacuum of 3 x 108 m/sec. c= f λ

Problem If a light wave’s frequency is 5.45 x10 14 Hz, what is its wavelength? What color light is it? Answer: 550x 10-9 m, green

Calculating the Speed of Light Danish Astronomer, Ole Roemer (~1668) found that the period of the moon of Jupiter , Io, varied depending on the location of the Earth. Distances were known. Estimated speed of light: 2.2 x108 m/s

Albert Michelson, American (1880’s) Measured time for light to make a round trip in California mountains 35km apart. Measured speed of light: 2.997996 x108 m/s First American to win Nobel prize.