Transcript PS6ElectricityMagnetism

Electricity
3 Methods for Charging Objects:
Friction, Conduction, and Induction
Human Hands (if very dry)
Leather
Rabbit Fur
Glass
Human Hair
Nylon
Wool
Fur
MORE
Lead
positive
Silk
Aluminum
Paper
Cotton
Steel (neutral)
Wood
Amber
Hard Rubber
Nickel, Copper
Brass, Silver
Gold, Platinum
MORE
Polyester
Styrene (Styrofoam) negative
Saran Wrap
Polyurethane
Polyethylene (scotch tape)
Polypropylene Vinyl (PVC)
Silicon
Teflon
FRICTION
Objects, when
rubbed, can
pick up net +
or - charges
+
+
+
+ + + + + + + + + + +
++ + + + + +
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Note: Fur is often used to give electrons, silk to remove
electrons!
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CONDUCTION
Charge is transferred by
objects contacting one
another
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INDUCTION
One object induces a charge on
another by rearranging charges on
another when nearby
(“induced dipoles”)
+ - + - + - + - + - + - + - + - + - +
+ - + - + - + - + - + - + - + - + - +
+ + + + + + + + + - - - - - - - - - -
+ + + + + + + + + + + + + + + + +
+ + + + + + + + + - - - - - - - - - -
+ + + + + + + + + + + + + + + + +
Simple Electric Circuit
V = Potential Difference = Voltage Difference(voltage)
in volts (V)
I = Current in amperes (A)
R = Resistance in ohms (Ω)
I = V/R (OHM’s LAW)
Series Circuit
What happens to the voltage and current if the number
of bulbs increases? The number of batteries?
Series Circuit 2
I = V/R
V = IR
[ORIGINAL (1 battery, 1 bulb)]
Voltage = V
Resistance = R
Current = I
[ADD 1BULB (1battery, 2 bulbs)]
Voltage = V
Resistance = 2R
Current = ½ I
[ADD 2BULBS (1 battery, 3 bulbs)]
Voltage = V
Resistance = 3R
Current = 1/3 I
As bulb number increases, bulbs are
individually dimmer!
Series Circuit 3
I = V/R
V = IR
[ORIGINAL (1 battery, 1 bulb)]
Voltage = V
Resistance = R
Current = I
[ADD 1 BATTERY (2 batteries, 1 bulb)]
Voltage = 2V
Resistance = R
Current = 2 I
[ADD 1 BATTERY (3 batteries, 1 bulb)]
Voltage = 3V
Resistance = R
Current = 3 I
As battery number increases, bulbs
are individually brighter!
Parallel Circuit
What happens to the voltage and current if the number
of bulbs increases? The number of batteries?
Parallel Circuit 2
I = V/R
V = IR
[ORIGINAL (1 battery, 1 bulb)]
Voltage = V
Resistance = R
Current = I
[Add 1 bulb (1 battery, 2 bulbs)]
Voltage = V
Resistance = ½ R
Current = 2 R
[Add 2 bulbs (1 battery, 3 bulbs)]
Voltage = V
Resistance = 1/3 R
Current = 3 R
As bulb number increases, individual bulb
brightness stays constant, but current
level increases, and power source is
drained more rapidly!
Parallel Circuit 3
I = V/R
V = IR
[ORIGINAL (1 battery, 2 bulbs)]
Voltage = V
Resistance = R
Current = I
[ADD 1 BATTERY (2 batteries, 2 bulbs)]
Voltage = 2 V
Resistance = R
Current 2 I
As the number of batteries is increased,
bulbs are individually brighter (all having the
same brightness), and current level
increases!
Can You Identify each of these
Circuit Types?
Component Connections
Ammeter – connected in SERIES with power source
Voltmeter – connected in PARALLEL in circuit
Note OPEN vs CLOSED CIRCUIT
Electrostatic charge Configurations
Equipotential
lines are blue
Electric Field
Lines are red
Temporary Magnets
Strength Variables
1) Material Used
Fe › Al, Pb, Cu, etc.
2) #strokes (in the same direction!) by
one pole of a
permanent magnet
#strokes … strength
Note: naturally magnetic elements
are iron(Fe), nickel(Ni), cobalt(Co),
neodymium(Nd), and gadolinium(Gd)
The “Rules” of Electrical/Magnetic Field Lines
Unmagnetized Material
Magnetized Material
1) Field lines form complete loops.
2) Field lines come out of the N pole, go into the S
pole.
3) The closer the lines, the stronger the field.
4) Field lines do not cross one another
Note: field lines point
away from N, toward S
Repulsion
Attraction
Earth’s Magnetic Field
Electromagnet
Variables:
1) Coil number
Cn# …strength
2) Current (I)
I …strength
3) Core material
Fe › Al, Pb, etc.
Notes: A solenoid is a
single wire wrapped
into a coil form; an
electromagnet is a
solenoid-wrapped iron
core
An electromagnet’s
properties can be
changed by controlling
it electrical current!
Motor
Changes electrical energy to mechanical energy
Motor Components
Wire coil
Permanent magnet
Power source
1. Brushes touch commutator…current flow…coil is attracted to
permanent magnet, rotates…
2. Brushes lose contact w/commutator…no current…inertia keeps
coil rotating…
3. Brushes contact opposite side of commutator…current reverses…
magnetic field reverses, flipping coil…
4. Brushes lose contact with commutator…etc…coil keeps rotating!
Generator
Changes mechanical energy to electrical energy
Generator Components
Wire coil
Permanent magnet
Outside energy source
1. Outside source causes coil to rotate through magnetic
field…current flow…
2. After first ½ turn, ends of coil wire move past the opposite
poles of permanent magnet…current changes direction…that’s
why the current produced is called alternating current (AC)!
OR
1. Fix the coil, and rotate the permanent magnet around it…etc
(Rotating magnets can be attached to a large wheel (turbine)
that rotates when pushed by water, wind, or steam)