Dec 30, 2015
Photo-Electric Effect Light causes a metal to eject electrons Amount of electron ejected depends on
frequency of wave not intensity Einstein’s explanation – photons
Energy of light exists in discrete bundles Nobel Prize in 1921
Photons – wave packet
Corpuscular theory of light Developed by Newton Light made up of small particles
(corpuscles) Traveled at finite speed
Christiaan Huygens Newton’s
contemporary Proposed wave
theory of light Rejected at time
because it countered Newton’s theory
Better explained interference, diffraction, and polarization
Mechanical waves need a medium to propagate
If light is a wave, does it need a medium to propagate? Space filled with a
luminous aether?
James Maxwell Developed equations
that synthesized electricity, magnetism, and optics
Light is the combination of an oscillating magnetic field (B-field) and an electric field (E-field)
Studied the orbit of Io The time it took Io orbit
varied depending on Earth’s position
Used the change in distance between Earth and Jupiter to measure the speed of light
Found that light takes 10-11 minutes to travel the radius of Earth’s orbit.
Romer’s speed of light ~ 2.5 x 108 m/s
Off by 17%
American physicist First American to win
Nobel Prize (1907) In 1924 found speed
of light to be 299,796 km/s
Two mirrors 22.5 miles apart
Octagonal mirror rotated at 528 rev/s
All light travels at the same speed c – speed of light c = 299,792,458 m/s c = 3.00 x 108 m/s c = λf
Light takes about 8 minutes to travel from the Sun to the Earth, how far is the Earth from the sun?
Lightning strikes 3 km (3000m) from your house. How long does it take for you to see the see lightning, and then hear it?
What is wavelength of an X-ray with a frequency of 7.7 x 107 THz?
In 1987 there was a supernova. The star was 1.59 x 1021 m away, how long had the light been travelling?