Today: Electromagnetic Waves

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Today Electromagnetic Waves
Extraterrestrial Life Review
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Electromagnetism
Properties of Charges 1 Charges come in
two types positive and negative 2 Like
charges repel unlike charges attract 3
Charge is discrete comes in increments of the
amount of charge on the electron.
4 Charge is conserved.
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Important things about charges 1 Stationary
charges produce electric fields.
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Magnetic fields the permanent magnet
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S
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Magnetic fields the coil
Moving charges are called currents (like water
currents).
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A disturbance in the field travels at the speed
of light c 3 x 108 m/s
Light is an electromagnetic wave!!!
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Summary
1 Stationary charges produce electric
fields 2 MOVING charges produce electric
magnetic fields 3 ACCELERATING charges produce
electric fields, magnetic fields, and
electromagnetic radiation (light)
Changing electric fields produce magnetic
fields Changing magnetic fields produce electric
fields
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TYPES OF ELECTROMAGNETIC RADIATION
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The Light Year The distance light travels in
one year.
r 3 x 108 m/s t 1 year 3.2 x 107 s
d r t 9.5 x 1015 m 9.5 x 1012 km
5.7 x 1012 miles 5,700,000,000,000 miles!!
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Our radio waves
Vega
Earth
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The star Vega (a candidate for a planetary
system) is 26 Light-Years away. They are
presently receiving our music and TV shows from
1979 The Bee-Gees, Threes Company, the Gong
Show, and Star Wars!
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If we have become technically advanced in order
to exploit electromagnetic waves in order to
communicate and transfer informationthen
extraterrestrials, if they exist, might be so
developed as well!
Should we be listening for them?
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WE ARE! The radio telescope at Arecibo, Puerto
Rico
There is so much data to be analyzed, that you
can get free software (looks like a screen saver)
that will help them you can get this at
http//seti.ssl.berkeley.edu/
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Can we estimate the chances that intelligent
extraterrestrial life exists in our galaxy?
We can do an order of magnitude calculation
Step 1 How many stars are in our galaxy?
about 4 x 1011 Stars
Note we are only going to estimate the number of
life supporting (sun-like) stars that are in OUR
galaxy. There are BILLIONS of other galaxies!!
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Some of those stars are DUAL star systems
About HALF of the stars are like thisthis is no
good for surrounding planets
We must divide the total number of possible stars
by 2.
Number 2 x 1011 stars.
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The star life cycle
The fraction of sun-like stars is only about 1/10.
Number 2 x 1010
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Only about 1/10 of these remaining stars even
have planetary systems Divide our number by 10!
Number 2 x 109
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If our solar system is good indicator only about
one in ten of the planets are Earth-Like (have
water and an atmosphere). We must divide our
number by 10
Number 2 x 108
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From experiments where the initial conditions of
early Earth were modeled, about 1 out of 100
would produce protein structures that could
develop into life forms. We must divide our
number by 100
Number 2 x 106 (Two Million)