Physics Mrs. Coyle

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 TV Microwave Infrared radiation Visible Light 700x x10 -9 Ultraviolet X-rays Gamma raysshorter than

Visible Light is detected by the human eye. red700 x (700nm) orange yellow green 550 x blue indigo violet 400 x (400nm)

Electromagnetic Spectrum

Speed of Light, c All EM waves have a speed through vacuum of 3 x 10 8 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 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 x10 8 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: x10 8 m/s First American to win Nobel prize.

Speed of Light (1983) Seventeenth General Congress on Weights and Measures measured: x 10 8 m/s We round to 3 x 10 8 m/s

Luminous Objects emit light. Illuminated Objects reflect light rays.

Luminous Flux, P Rate at which light is emitted from a source. Unit: lumen, lm

Illuminance, E, measures illumination of a surface. E = (Luminous flux P) (area around source) E= P / (4πd 2 ) d : distance from source Unit: Lumens/ m 2 =lux=lx

Problem A lamp is moved from 20cm to 40cm from a book. Compare the illumination before and after.

Candela (candle power) Luminous intensity of a point source is the luminous flux that falls on 1m 2 of a sphere of 1 m radius. cd = Luminous flux/π One of the fundamental SI units