Transcript Slide 1

How fast is that?
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299 792 458 m / s or 3.00*108 m/s
Around the Earth 8 times in one second
1.5 seconds to the Moon
4 minutes to Mars
8 minutes to the Sun
30 minutes to Jupiter
4.24 years to the NEAREST star
Light Year
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One light-year (ly) is the distance that
light travels in a year
9.46 × 1015 meters
About 6 trillion miles
Yes, that’s FAST!
Solar System Travel
Time to
Speed
Time to Jupiter
α Cen
Freeway Speed
75 mph
600 yrs
38 million yrs
Jetliner Speed
500 mph
90 yrs
6 million yrs
Concorde Speed
(Mach 2)
1350 mph
33 yrs
2 million yrs
Spacecraft Speed
(Voyager)
40,000 mph
1.5 yrs
70,000* yrs
Way Big
Our Milky Way Galaxy is only
100 000 light years across or about
600 000 000 000 000 000 miles or
6 x 1017 miles or
9.5 x 1017 km or
9.5 x 1020 meters or
950 000 000 000 000 000 000 meters
What is light?
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Light is an electromagnetic wave
Oscillating electric and magnetic fields
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Oscillations are in phase
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In phase--When Electric field is increasing, Magnetic field is
increasing.
When E field is decreasing, Magnetic field is decreasing
More on EM wave
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Electric and magnetic fields are perpendicular
to each other and the direction of travel
Transverse wave
You might have heard…
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…that light acts as both particle and
wave
It does, but for most of this class, light
is a wave.
White Light
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White light is made of a range of
frequencies or colors
Can be separated into six elementary
colors of the visible spectrum
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Spectrum—The distribution of wavelengths
and frequencies
Visible light
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Visible Spectrum—Red, Orange, Yellow,
Green, Blue, and Violet.
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Indigo was demoted :<(
Roy G. Bv
EM Spectrum
Speed of EM waves
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All EM waves travel at 3.00*108 m/s
Energy of EM waves depends on frequency.
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Gamma rays=HIGH energy, radio waves=low
energy
Speed of the wave depends only on the
medium - constant in a constant medium
Water 75% Glass 67% Diamond 41%
Nothing can travel faster than light in a
vacuum
Measuring speed of light
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Galileo was one of the first to try
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Tried to determine time it took light to
travel 1.5 km. Would he be able to
measure the speed?
Now, error is less than .0001%
Wave Speed Equation:
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c=fλ
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Speed of light=frequency x wavelength
Example
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Red light has a wavelength of 750nm.
What is the frequency? c=3.00*108 m/s
First, 750nm = 750*10-9 m =
7.5*10-7 m
Plug into c=fλ
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(3.00*108 m/s) / (7.5*10-7 m) = f
f=4.0*1014 Hz