light … is an electromagnetic wave: … is a wave pattern of electric and magnetic fields …...
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Light … is an electromagnetic wave:Light … is an electromagnetic wave: • … is a wave pattern of electric and magnetic fields• … propagates in vacuum• … has wavelength (blue: 400 nm, red: 700 nm)
The physics of light
1 mm = millimeter
1000 m = 1 mm
1000 nm = 1 m
Micrometer(size of a germ)
Nanometer(size of ten atoms)
LearnLearnunits of distance!units of distance!
0.4 m 0.7 m Millimeter
(size of ant)
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Olaf Römer
Speed of light c = 300,000 km/s: Discovered by: Olaus Roemer (1675)
• Eclipses of Jupiter’s moons come a few minutes late when Jupiter is on the far side of its orbit.• Reason: light needs extra time to reach us.• Conclusion: light needs 9 minutes to traverse the Sun-Earth distance.
Watch07JupiterMoonDance.mov
Light takesLight takes • a few minutes/hours to move around in the solar system• years or more to go from star to star
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The electromagnetic spectrum
Light has a wavelength:
Wavelength of light means color:
• Blue has short wavelength• Red has long wavelength
What isbeyond blue?
Bluer than blue is UV (ultraviolet) - even shorter wavelengthRedder than red is IR (infrared) - even longer wavelength
These are colors of light invisible to the eye.
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The full spectrum
And what is beyond those wavelengths?And what is beyond those wavelengths?
(A prism breaks up white light into colors.)
They all move with the same speed c = 300,000 km/s
Radio | Infrared | Visible | Ultraviolet X-ray| -ray
Need spacecraft(Far UV, X-ray, -ray)
Need spacecraft
Eye / TelescopeRadio antenna
PrismSlit
White light
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Questions coming …
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30Question 11 29Which one is moving fastest?
A Radio waves
B X-rays
C Visible light
D Laser
E The same
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Next question coming …
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30Question 12 29What is the difference between red and blue light?
A Intensity.
B Speed.
C Wavelength.
D Blue is composite, red is not.
E Red is existence of light, blue is lack of light.
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45Question 13 403530252019181716151413121110 9 8 7 6 5 4 3 2 1 0
Next question coming …
How many of the following types of “light” penetrates the atmosphere?
• Radio waves • Far IR • Regular light • Far UV • X-rays
A 1 B 2 C 3 D 4 E 5
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30Question 14 29How was the speed of light measured for the first time?
A In an experiment with a laser beam.
B By the time delay the astronauts’ answer came from the Moon.
C Observing the moons of Jupiter.
D By measuring the radar signal reflected by the Moon.
E By measuring the time light takes to arrive to usfrom another galaxy.
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Structure of atom
Recall: Chemistry cannot change the nucleus, only bind atoms into molecules
Isotopes: same number of p and e, different n. Same chemical properties.
Examples: H: 1 p 0 n 1 eDeutron: 1 p 1 n 1 e (same as H but heavier)
He: 2 p 2 n 2 e