chapter 27 properties of light light photons electromagneticradiation
TRANSCRIPT
Chapter 27Chapter 27Properties of LightProperties of Light
LightLightPhotonsPhotons
ElectromagneticElectromagneticRadiationRadiation
These three are the same…
• Light * pure energy
• Electromagnetic Waves* energy-carrying waves emitted by vibrating
electrons
• Photons* particles of light
Electromagnetic Electromagnetic Wave VelocityWave Velocity
• The speed of light is the same for all seven forms of light.
• It is 300,000,000 meters per second or 186,000 miles per second.
Michelson’s 1878 Rotating Mirror Experiment
Picture credit
• German American physicist A.A. Michelson • Using this method, Michelson was able to calculate c = 299,792 km/s
The Electromagnetic The Electromagnetic SpectrumSpectrum
• A range of light waves extending in wavelength from radio waves to gamma rays
The Electromagnetic The Electromagnetic SpectrumSpectrum
• Radio Waves - communication
• Microwaves - used to cook
• Infrared - “heat waves”
• Visible Light - detected by your eyes
• Ultraviolet - causes sunburns
• X-rays - penetrates tissue
• Gamma Rays - most energetic
The Visible SpectrumThe Visible Spectrum
•A range of light waves extending in wavelength from about 400 to 700 namometers.
Questions• Is it correct to say that radio
wave is a low-frequency light wave?
• Is a radio wave also a sound wave?
• See question on page 455.
*
Transparent Transparent MaterialsMaterials
• Transparent - the term applied to materials through which light can pass in straight lines
Opaque Opaque MaterialsMaterials
• Opaque - the term applied to materials that absorb light
Example QuestionsExample Questions• Are clouds transparent or opaque to
visible light?• Answer: opaque
• Are clouds transparent or opaque to ultraviolet light?
• Answer: transparent
ShadowsShadows
• Umbra - the darker part of a shadow where all the light is blocked
• Penumbra - a partial shadow
• These terms also apply to Solar Eclipses and Lunar Eclipses.
Penumbra
Umbra
Partial Shadow
Full Shadow
Solar Eclipse
Sun
Moon
Earth
• A solar eclipse occurs when the Moon passes in front of the Sun.
Lunar Eclipse
Sun
EarthMoon
• A lunar eclipse occurs when the Moon passes into the Earth's shadow.
Polarization
Electric field only goingup and down – say it islinearly polarized.
Light can have other types of polarizations such as circularly polarized or elliptically polarized. We will only look at linearly polarized light.
Net electric field is zero – Unpolarized light!
How do we make Polarized Light?
I. Polarizers-
Polarizers are made of longchained molecules which absorblight with electric fields perpendicular to the axis.
• Light is totally polarized when an object with a vertical Polarization axis and another object with a horizontal polarization axis are placed next to each other.
• This causes no light to be able to get through the lens.
Questions• Which type of eclipse is
dangerous to view with the unprotected eye?
• Why are lunar eclipses more commonly seen than solar eclipses?
• See question on page 460.
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Chapter 27 Review Questions
You will observe a total eclipse of the sun when...
(a) you stand in the penumbra of the moon’s shadow
(b) you stand in the umbra of the moon’s shadow
(c) sunlight diffracts around the moon
(d) sunlight reflects from the moon to the earth
(b) you stand in the umbra of the moon’s shadow
The speed of light...
(a) has never been measured
(b) is about the same as that of sound
(c) is infinitely fast
(d) is very fast, but not infinite
(d) is very fast, but not infinite
In the dark at late evening, no color is seen because of lack of stimulation of
a. rods.
b. cones.
c. cornea.
d. crystalline lens.
b. cones.
End of Chapter 25