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

Matter has wavelike properties Significant for very small masses

(electrons) Quantum Mechanics

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)

Galileo 1630s Two lanterns on two

mountains Ole Romer

1676 Astronomical

calculation

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?