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Chapter 7
Electricity
What is Charge?
Protons have a (+) charge
Opposite Charges Attract
Electrons have a (-) charge
Charge (q) is measured in
Coulombs
The elementary charge of one (+)
or (-) is 1.6 x 10-19 C
1 Coulomb = 6.25 x1018 electrons
Like Charges Repel
Static Electricity
the accumulation of excess electrons on an
object
Current
The flow of charges, usually electrons,
through a wire or conductor is called
electric current
Electric current is measured in amperes (A).
Potential Difference is the push that
causes charges to move.
Voltage is measured in Volts (V)
Resistance
The greater the restriction of charges to
flow the lower the amount current that
can flow.
Resistance is measured in ohms (Ω)
The length, diameter, and temperature of
a wire influences it’s resistance.
Types of resistors:
Light bulbs
Door bells
Any electrical device
Types of Currents
Direct Current
(dc) is the type of
electricity that we
get from batteries.
In a direct current
all of the electric
charges move in
one direction.
Types of Current
Alternating Current
(ac) is the type of
electricity that we
get from plugs in the
wall.
In an alternating
current all of the
electric charges
switch their
direction of flow
back and forth.
Ohm’s Law
Ohm’s Law – the
current in a circuit
equals the voltage
difference divided
by the resistance.
V=IR
I=V/R
R=V/I
Ohm’s Law
I = Current (Amperes)
V = Potential
Difference (volts)
R = Resistance (ohms
Ω)
Circuits
Total Resistance in Circuits
Series
Parallel
RS = R1 + R2 + R3 + …
1/RP = 1/R1 + 1/R2 +1/R3 +…
Total resistance increases as more
Total resistance decreases as more
resistors are added to the series circuit
resistors are added to the parallel circuit