Download 9 Electricity Notes

Chapter 6 & 7: Electricity
Electricity
• The flow of electric current.
• The flow of electric energy carried by
electrons.
Electric Circuits
• something that provides a path through
which electricity travels
• Made up of wires, switches, resistors,
capacitors, etc.
Open/Closed Circuits
• Open Circuit: a circuit in which there is a
break in the wire so that current cannot
flow,; a switch turned to the "off" position is
one way to cause the break in the wire
• Closed Circuit: a circuit in which the
switch is turned to the "on" position,
causing there to be no breaks anywhere in
the wire
Short Circuit
• Is usually an accidental extra path for
current to flow.
• Can cause excess electrical energy to flow
through parts of the circuit causing
overheating of wires.
Electrical Charge
• Positive Charge-associated with protons.
• Negative Charge- associated with
electrons.
• Like charges repel.
• Opposite charges attract.
• Amount of charge is measured in
coulombs.
Static Electricity
• Build up of electrical charges on an
insulator.
• Electrical charge doesn’t move.
Voltage
• The amount of potential energy that each
unit of electrical charge has.
• The amount of push behind the electrical
energy.
• Measured in volts using a voltmeter
Current
• Is the flow of electric charges.
• Measured in amperes (amps for short)
using an ammeter.
– Coulombs per second
AC/DC
• Alternating Current- current in which the
direction changes back and forth.
• Direct Current- current flows in only one
direction.
Resistance
• Electrical Conductor: materials which the
charge flows very easily
• Electrical Insulator: materials which block
the flow of electricity.
Resistance of Wires
• Larger diameter wires have less
resistance than thinner wires.
– A smaller gauge wire is thicker than a larger
gauge wire.
• Shorter wires have less resistance than
longer wires.
Ohm’s Law
• For a given voltage, the amount of current
in a wire is inversely proportional to the
resistance.
• V=I*R
• Not all materials obey Ohm’s law
– Diodes are examples of electrical components
that do NOT obey Ohm’s law.
Electrical Power
• P=V*I
– substituting I*R for V,
– P = I2 * R
Electrical Safety
• Fuses, circuit breakers, & GFI outlets are
used to prevent excessive amounts of
current flowing through a circuit.
• This will prevent wires from overheating
and causing a fire.
• Check the rating on extension cords
before using them.
Series Circuit
• The current can only take one path.
– IT = I1 = I2 = I3 …
• The total voltage drop across the circuit is
the sum of all the changes in voltage.
– VT = V1 + V2 + V3 …
• The equivalent resistor replacing all the
resistors is the sum of the total resistance.
– RT = R1 + R2 + R3 …
Parallel Circuit
• The current has multiple paths.
– IT = I1 + I2 + I3 …
• The voltage drop across the circuit is the
same across each branch.
– VT = V1 = V2 = V3 …
• The equivalent resistor replacing all the
resistors is the sum of the total resistance.
– 1/RT = 1/R1 + 1/R2 + 1/R3 …