PHYSICS 20B Lecture Notes - Lecture 6: V Speeds, Wind Wave
Lecture 6
Light in the Universe
● Light
○ Light is an electromagnetic radiation
○ It carries energy
○ Moves very fast
■ c=300,000 km/s in empty space
■ Speed changes in water, glass, or ice (slower)
■ The distance between the Earth to the Moon is 384,000 km, this means
that light can travel from Earth to the Moon in 1.28s
○ When crossing from one material to another (a person’s shadow when leaning
against a wall) light rays bend (refract) (the shadow starts on the ground, then
bends at the corner of the wall and ground, then the shadow continues on the
wall)
■ This is how lenses work
● Light beyond the visible
○ Just like the album cover fro Pink Floyd, white light splits into colors after passing
through a prism
■ Each color corresponds to a different wavelength of light
■ Because we know lights have wavelengths, that means there could be
other types of light we cannot see because of the frequency of the
wavelength
○ In 1800, a man named William Herschel discovered infrared light
○ Infrared light has a wavelength longer than the lights that are visible , thus which
is why we can’t see it.
● Herschel’s Experiment
○ What Herschel did to acknowledge infrared light, was through the use of
thermometers
○ He had a prism in which the light was shown on a table. He placed thermometers
in line parallel to the light. With this, he knew that light gave of a temperature,
and thus there would be light. Then he decided to measure the temperature just
beyond the red portion of the spectrum, a region where no light was visible, and
found that regions beyond red had the highest temperature of all, this meant that
there is light beyond the red portion we can not see, but do indeed exist.
● TYpes of light
○ Gamma-rays, x-rays, ultraviolet, visible, infrared and radio waves are all types of
electromagnetic radiation, or “light”
○ One difference between these lights are its wavelength
○ Wavelength and frequency are related by speed of light
■ frequency : V
● Number of times per second that a crest passes a fixed point
■ 1 wavelength is measured in lambda, an upside down y symbol.
● Lambda x V = speed of light = c
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Document Summary
Speed changes in water, glass, or ice (slower) The distance between the earth to the moon is 384,000 km, this means that light can travel from earth to the moon in 1. 28s. Just like the album cover fro pink floyd, white light splits into colors after passing through a prism. Each color corresponds to a different wavelength of light. Because we know lights have wavelengths, that means there could be other types of light we cannot see because of the frequency of the wavelength. In 1800, a man named william herschel discovered infrared light. Infrared light has a wavelength longer than the lights that are visible , thus which is why we can"t see it. What herschel did to acknowledge infrared light, was through the use of thermometers. He had a prism in which the light was shown on a table. He placed thermometers in line parallel to the light.
