Electricity

A.  Electric Charge

1.  Static electricity

a.  The accumulation of electric charges on an object.

b.  Static means they do not flow.

c.  Only electrons (-) can move; protons (+) cannot move.

d.  More electrons than protons means an overall negative charge; more protons than electrons means a positive charge.

e.  The law of charges states that opposite charges attract and like charges repel.

f.  An electric field is the area around a charge that affects any other charge; it gets weaker with distance.

2.  Conductors are materials that allow electrons to move through them easily.

3.  Insulators are materials that do not allow electrons to move easily through them (but electrons can move through any insulator).

4.  Objects are grounded if they are connected to the earth.

5.  The electroscope is a device that detects the presence of electric charges.

6.  One coulomb is the unit for the amount of charge carried by 6.24 billion billion electrons.

B.  Lightning - see handout.

C.  Electric Current

1.  Current electricity is a continuous flow of electrons through a circuit.

2.  Current

a.  The unit is the ampere, or amp (A).

b.  One amp equals one coulomb of charge that passes a point in one second.

c.  Amps are how much charge passes a point in a second.

d.  The ammeter is the instrument used to measure current.

3.  Voltage

a.  Voltage is the difference in electrical potential between two places that electrons are flowing.

b.  Electrons always flow from higher potential to low potential.

c.  Unit is the volt.

d.  The voltmeter measures voltage.

4.  Something must keep current moving through a circuit (an electron pump).

5.  Batteries generate current by a chemical reaction.

a.  Dry cells are batteries have electrolytes in the form of paste.

1)  Flashlight batteries

2)  More cells connected together make higher voltage.

b.  Wet cells are batteries that have a liquid electrolytic solution.

1)  Car batteries

2)  Sulfuric acid is a major component.

D.  Resistance

1.  Resistance is a material's resistance to the flow of electrons through it.

2.  Unit is the ohm.

3.  Measured using an ohmmeter.

4.  Factors that affect resistance:

a.  Temperature (colder = less resistance & visa versa)

b.  Thickness of the wire (thicker = less resistance & visa versa)

c.  Length of the wire (shorter = less resistance & visa versa)

5.  Superconductors are materials that are cooled extremely low and have virtually no resistance.

6.  Ohm's law

a.  Potential difference = current x resistance

b.  V = I x R

E.  Electrical Circuits

1.  Closed circuits allow electricity to flow; open circuits do not.

2.  Series circuits

a.  Have only one pathway for the electrons to follow.

b.  Any break will cause all devices to go out.

c.  The more devices in series, the less energy each one receives.

3.  Parallel circuits

a.  Have separate branches for current to move through.

b.  A break in one branch does not affect devices in other branches.

c.  Every device gets the same amount of energy.

4.  Safety devices

a.  Fuses melt to open a circuit and keep it from overheating.

b.  Circuit breakers contain a metal strip that bends when it gets too hot; this opens the circuit and can be reset.

F.  Electric Power and Energy

1.  Electrical power is the rate at which electricity is converted into another form of energy.

a.  Power = current x voltage

b.  P = I x V

c.  Unit is the watt or kilowatt

2.  Electrical energy

a.  Energy = power x time

b.  E = P x t

c.  Unit is the kilowatt-hour (kWh)

G.  Light Bulbs

1.  Incandescent

a.  Have a tiny filament that resists the flow of electrons through it.

b.  The filament gets hot and glows to produce light.

c.  These bulbs are very hot and inefficient.

2.  Fluorescent

a.  Tubes are filled with a gas and the inside is coated with phosphor.

b.  Electricity excites the gas particles and makes them give off U-V rays.

c.  The phosphor absorbs the U-V rays and glows to produce light.

d.  These bulbs are very cool and efficient.