Electricity

3 Methods for Charging Objects: Friction, Conduction, and Induction

Human Hands (if very dry) Leather Rabbit Fur Glass Human Hair Nylon Wool Fur Lead Silk Aluminum Paper Cotton Steel (neutral) Wood Amber Hard Rubber Nickel, Copper Brass, Silver Gold, Platinum Polyester Styrene (Styrofoam) Saran Wrap Polyurethane Polyethylene (scotch tape) Polypropylene Vinyl (PVC) Silicon Teflon 

MORE negative

MORE positive

FRICTIONObjects, when rubbed, can pick up net + or - charges

+ + + + + + + + + + +

+ + + + + + +

+++

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

Note: Fur is often used to give electrons, silk to remove electrons!

CONDUCTIONCharge is transferred by objects

contacting one another

_ _ _ _ _ _ _ ____

_ _ _ _ _ _ _

_ _ _ _ _ _ _ _ _ _

INDUCTIONOne 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 = RCurrent = I

[ADD 1BULB (1battery, 2 bulbs)]Voltage = V

Resistance = 2RCurrent = ½ I

[ADD 2BULBS (1 battery, 3 bulbs)]Voltage = V

Resistance = 3RCurrent = 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 = RCurrent = I

[ADD 1 BATTERY (2 batteries, 1 bulb)]Voltage = 2V

Resistance = RCurrent = 2 I

[ADD 1 BATTERY (3 batteries, 1 bulb)]Voltage = 3V

Resistance = RCurrent = 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 RCurrent = 2 R

[Add 2 bulbs (1 battery, 3 bulbs)]Voltage = V

Resistance = 1/3 RCurrent = 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 = RCurrent = I

[ADD 1 BATTERY (2 batteries, 2 bulbs)]Voltage = 2 V

Resistance = RCurrent 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 sourceVoltmeter – connected in PARALLEL in circuit

Note OPEN vs CLOSED CIRCUIT

Electrostatic charge Configurations

Equipotential lines are blue

Electric FieldLines 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

ElectromagnetVariables:

1) Coil numberCn# …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!

MotorChanges electrical energy to mechanical energy

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!

Motor Components

Wire coilPermanent magnet

Power source

GeneratorChanges mechanical energy to electrical energy

Generator Components

Wire coilPermanent 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)!

OR1. 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)