Light/Waves

Decoding Light

• Light-
• can travel billions of light years
• brings information about its origin
• Lenses and mirrors to manipulate light was already known to Egyptians, Mesopotamians, and Greeks
• Islamic scholars added geometrical optics, and suspected it has finite speed
• Is light particles or a wave?

Directional Astronomy

• Light takes time to travel
• The further/closer and object is determines when we see its "light"
• c = 300,000 km/s

Sunlight is a mixture of all colors

• prisms don't add colors, but rather light bends and separates into an array of colors
• a second prism will combine the light back to white
• spreading (dispersing) light according to colors is called a spectrum
• Different color sunlight raises temperature by different amounts
• putting photographic paper beyond the blue shows the strong chemical reaction
• invisible light also comes from the sun!

Disturbance

• traveling disturbance - carrying energy
• -sound
• -stadium audience
• -water surface
• -earthquakes
• -light

Simple Waves

• Transverse - up/down
• though to through = wavelength
• Longitudinal - along (compression/expansion)
• compression to compression = wavelength
• material affects waves
• always moves through a medium
• needs connection to travel

tranverse

• 300 km/s
• particles do not get displaced, but go up/down
• motion of disturbance ----->

Longitudinal

• particles oscillate around one fixed point

diffraction

• wave "bends"
• amount of bending depends on the relative size of the wavelength and the opening
• only waves show diffraction, not particles

interference

• waves crossing each other will interfere with each other
• destructive (close to opposite/different)
• constructive (matching or similar)
• cancel out (opposite)

Polarized

• can cancel out light waves
• will not affect particles

What kind of disturbance is light?

• light can travel in vacuum and what its frequency is
• that speed is constant: c = 3 x 10^5 km/s
• changing magnetic field generates electricity, and that change in the electric field creates magnetism - synchronized change of these fields is electromagnetic radiation, or light - carries energy
• transfers from magnetic field to electric field to travel
• how often it goes from one maximum to the next maximum is called frequency
• c = (lambda)*(frequency)
• speed of light = length*time
• speed = d/t
• d = (1/time)

another wave that doesn't need medium

• gravitational waves
• also has constant speed (speed of light)
• c = 3*10^5 km/s
• look up how Einstein is relevant

Photoelectric effect

• decrease amplitude of sound and it disappears
• the right type of light can displace light (caused by increasing intensity/frequency of light thus increasing electrons)
• E (of a photon) = h*f = h*(c/lambda)
• E = h*f or E = m*c^2 so the photon has mass
• 1921 Nobel Prize for Einstein

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