Transcript 0415light.ppt.pptx

Light
Students will learn about light.
Light
• Light is a transverse electromagnetic wave.
Consider the electric field portion as
transverse up and down and the magnetic
field portion as perpendicular side to side.
• Light has many wave properties: reflection,
refraction, diffraction, interference patterns,
Doppler effect, color dependent on frequency,
and intensity (or brightness) dependent on
the amplitude of the waves.
Speed of light
• The speed of light in a vacuum (and also in air)
is 3 x 10^8 m/s.
• Albert Einstein showed that nothing,
nowhere, no how can ever every go faster
than the speed of light = 3 x 10^8 m/s.
Light as a particle
• Sometimes light acts as a particle
• Light “particles” are called “photons”
• In very dim light, light appears as small pieces
or bits
• Light energy (as photons): E = hf
– H = 6.63 x 10^-34 Joule seconds
Electromagnetic Spectrum
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Gamma rays
X rays
Ultraviolet
Visible
Infrared
Microwave
FM/TV
AM
10^19 – 10^21 Hertz
10^17 – 10^20 Hertz
10^15 – 10^18 Hertz
10^14 – 10^15 Hertz
10^12 – 10^14 Hertz
10^9 – 10^12 Hertz
10^8 Hertz
10^6 Hertz
10^-12 m
10^-10 m
10^-7 m
10^-6 m
10^-5 m
.01 m
3m
200 m
Dispersion
• Dispersion is the spreading of white light into
the full spectrum. A prism separates white
light into a rainbow of colors. This happens
because the index of refraction of the material
depends on the wavelength. Different
wavelengths are bent to varying degrees.
• Violet is bent the most; red is bent the least.
• The sky is blue because it is bent the most as
sunlight comes through earth’s atmosphere.
Examples of Dispersion
• Prism
• Rainbow
• Diamonds
Polarized light
• Ordinary light is unpolarized. It has many
vibrations in many planes at once. The
electric field vectors vibrate at all angles.
• Light can be “filtered” or “polarized” by
passing it through parallel slits. Long
molecules can be arranged as long slits to
achieve this purpose.