Physics Gang Signs Review

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Transcript Physics Gang Signs Review

Physics Gang Signs Review
1. If your were a positively charged particle
headed toward the Earth’s equator from outer
space which way would the Earth’s magnetic
field force you?
B-field =
v=
q=
so the Force =
2. If you were moving toward the Earth at
either pole then what would happen?
• NOTHING. . .the direction of the velocity and the B-field are
parallel to each other so NO FORCE is felt!!
(This is what causes the Northern and Southern Lights.)
• Electrons from solar wind interact with the nitrogen and oxygen in the
atmosphere anywhere from 20 to 200 miles above the surface of the
Earth
COLORS of auroras:
O2 = Green (up to 150 miles) Red (above 150 miles from surface)
N2 = Blue (up to 60 miles) Purple (above 60 miles from surface)
Michael Faraday
• The discovery that an electric current in a wire
produced magnetism was a turning point in
history.
If a Current creates
a Magnetic Field ...
BI
... Can a Magnetic
Field cause electric
current?
I
Faraday’s Contribution
• Discovered the electric current could be
produced in a wire by simply moving a magnet
in or out of a wire coil.
• No battery or other voltage source was
needed.
• The amount of voltage produced depends on
how quickly the magnet passes through coil of
wires.
– It doesn’t matter if it’s the magnet moving
through the coil or visa versa.
Electromagnetic Induction
• ANY CHANGE in a MAGNETIC FIELD, will
create an ELECTRIC CURRENT
• Inducing voltage by changing the magnetic
field around a conductor is electromagnetic
induction.
Faraday’s Law
Faraday’s Law says that you can create (induce)
more voltage by
1) moving the B-field faster
2) moving it into and out of more coils of wire
**the amount of current produced by electromagnetic
induction depends not only on the induced voltage but the
resistance of the coil and circuit to which it’s connected.**
Generator and AC current
• A GENERATOR uses electromagnetic induction, it turns
mechanical energy into electrical energy.
• As the coil enters the magnetic field, voltage is induced one
direction, as the coil leaves the magnet, voltage is induced
the other direction.
– This produces current that travels one direction in a wire, and then
switches directions as the magnet leaves the coil = AC current
Transformers
• Uses Faraday’s Law and ferromagnetic properties of an iron
core to raise and lower AC voltages.
• Used to transfer electric energy from one circuit to another.
How it works
• Current passes through primary, as a result, current passes
through the secondary.
• Iron core guides B-field lines from primary through the
secondary.
• Voltage of primary is passed to EACH loop of secondary.
– Twice as many loops, twice the voltage produced in secondary
– Three times the loops, three times the voltage produced
Equation
• Relationship between the voltages is with
respect to the number of turns of the wire.
Vp
Vs

np
ns

Ip
Is
Energy transferred
• The coil transfers energy from one coil to another
• The rate at which energy is transferred is POWER
– The primary gives no more power than the second uses (COE)
REMEMBER:
P = VI
IN TRANSFORMERS
PIN = POUT
VIIN = VIOUT
Step Up and Step Down transformers
• Transformers are also used to raise and lower the voltage
to meet certain operating requirements
• The ratio between the number of turns in the primary
and the secondary is called the Turns Ratio
I1
PRIMARY
I2
SECONDARY PRIMARY
SECONDARY