Electricity

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Electricity A. Electric Charge 1. Static
electricity is the accumulation of excess
electric charges on an object. a. More e
negative charge b. More protons
charge 2. Charge is conserved (e move from one
object to another).
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3. Law of Charges
a. Opposite charges attract. b. Like
charges repel.
4. Electric fields
a. Electric fields exert force on objects
within the field. b. Weaker with distance.
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5. Transferring electric charge a.
Conductors e move easily. b. Insulators
hold e tightly.
c. Contact charging is done when two
materials are rubbed together (best with
insulators).
d. Charging by induction is done when one
charged object induces a charge on another.
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6. Lightning a. Large static discharge
between the earth and clouds. b. Lightning
was found to be static electricity by Ben
Franklin.
7. Grounding a. Conductive path to Earth.
b. Lightning rods plumbing.
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8. The electroscope can be used to detect
electric charge
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B. Electric Current 1. The reason electric
charge flows from one place to another is voltage.
HIGH
LOW
a. Voltage is the difference in electrical
potential between two places where e are
flowing. b. Voltage is the push that makes
electric charges move. c. Measured in volts
(V).
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2. The flow of electric charge is called
current. a. Current is measured in amperes,
or amps (A). b. Voltage causes current. 3.
The amount of electric charge is measured in
coulombs. a. 1 coulomb is the charge carried
by 6.24 x 1018 e. b. 1 amp is 1 coulomb
per sec.
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4. Batteries are e pumps. a. They provide
a voltage difference to a circuit. b.
Types wet-cells dry-cells
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5. Resistance a. Opposition to the flow of
e.
b. It changes electrical energy into thermal
energy and/or light. c. Measured in ohms.
d. Conductors have less resistance than
insulators.
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e. Wire resistance greater for 1)
Longer wires 2) Thinner wires
3) Higher temperatures
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6. Ohms law
Voltage Difference Current
Resistance
V
I
R
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C. Electrical Circuits 1. A circuit is a
conducting path.
2. Series circuit a. One path b. Any
break all devices go out

c. Current is the same throughout the
circuit
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Series Circuit Concepts (assuming 3 resistors)
RTOTAL R1 R2 R3 V drop for each R is VX
I RX so, VTOTAL I R1 I R2 I
R3 or, VTOTAL I (R1 R2 R3) since
I V R then ICIRCUIT V (R1 R2 R3)
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3. Parallel circuit a. Multiple paths
b. A break in one branch the other branches
stay on
c. Voltage is the same in each branch, but
current and resistance may be different
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Parallel Circuit Concepts (assuming 3 paths)
V is the same everywhere in the circuit ITOTAL
I1 I2 I3 since ITOTAL V R and I1 V
R1 then V R V R1 V R2 V R3
1 1 1 1 RTOTAL R1 R2 R3
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Comparison of series and parallel circuits
The same voltage battery
Notice the brightness of the bulbs
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4. Household circuits
a. Mostly parallel. b. 120 V in the
U.S. c. More devices plugged in a circuit
mean more current. d. More current means
more heat in the wiring.
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5. Electrical safety devices
a. Fuses - one time use. b. Circuit
breakers - can be reset and reused.
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D. 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. Unit is the
watt or kilowatt. 2. Electrical energy a.
Energy power x time b. Unit is the
kilowatt-hour. (1000 watts for 1
hour) c. This is what we buy from the
electric company.
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E. Light Bulbs
1. Incandescent a. Have a tiny filament
that resists the flow of electrons. b. The
filament gets hot and glows to produce light.
c. Very hot and inefficient.
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2. Fluorescent
a. Filled with gas and coated with phosphor.
b. Electricity excites the gas
making it give off U-V rays. c. Phosphor
absorbs U-V rays and glows to make light. d.
Very cool, efficient, and last a long time.