chapter 5

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University of Toronto St. George
Astronomy & Astrophysics
Stefan Mochnacki

20:46 5.1 light in everyday life Telescopes collect light of distant objects and astronomers extract info from the light Sunlight transfers energy to the molecules in your skin Energy in light is radiative energy Rate of energy flow = power; measured in units of watts 1 watt = 1 joules prism split light into rainbow of light = spectrum basic colors are red, orange, yellow, green, blue, violet white = basic colors mixed in abt equal proportion (all colors of rainbow) black = we perceive when there is no light, no color primary colors of vision = red, green, blue diffraction grating, piece of plastic or glass etched with many closely spaced line 4 ways light interact emission: eg. Light bulb emits visible light, energy of light from electrical potential energy supplied to light bulb absorption: your hand absorbs light when placed on light bulb, light bulb then warms your hand materials that absorb light are opaque transmission: some forms of matter, like glass or air, transmit light which means allows it to pass through materials that transmit light are transparent reflectionscattering: reflection bouncing in same general direction or scatter (bouncing is more random) red glasses transmits red light but absorbs all other color green lawn reflects green light but absorbs all other color 5.2 Properties of light particle is a thing can sit still or it can move from one place to another waves pattern revealed by its interaction with particles waves carry energy outward from one place to another consists of wavelengths (distance from one peak to the next), frequency (number of peaks passing by any point each second, measured cycles per second aka hertz), speed (how fast the energy travels from one place to another) wavelength X frequency = speed Energy = h X frequency of photon h plancks constant, 6.626 X 10 -3joules X s) light waves are vibrations of both electric and magnetic fields caused by the motions of charged particles light is a electromagnetic wave all light travel at the same speed, c= 300,000 kms
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