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What happens connect the two
ends of a battery with a wire?
• The negative terminal of the battery acts
as though it has too many electrons. That
is, it acts like it is negatively charged. So,
the negative terminal of the battery pushes
electrons in the wire away and toward the
positive terminal.
• In a closed loop, the result is a flow of
electrons through the wire.
Electric Current
Electric current (or just current) is the rate at
which charges (electrons) flow through a
wire.
More generally, currently is the rate at which
charges flow through a surface.
The unit for current is the Amp 1 A=1 C/s
The symbol for current is i
The current through a circuit (and
so through the battery) changes
when we change the number of
bulbs in the circuit or how they
are arranged.
Bulbs present an obstacle
(or resistance) to the flow of current.
Bulbs Don’t Use Up Current
• Why do batteries go “dead”?
For a given battery:
• The current is the circuit is not always the
same.
• More resistance in the circuit,
current
in the circuit.
• Less resistance in the circuit,
current.
For a given battery:
• The current is the circuit is not always the
same.
• More resistance in the circuit, less current
in the circuit.
• Less resistance in the circuit, more current
in the circuit.
• Does adding bulbs increase or decrease
the total resistance in the circuit?
More Bulbs Changes the Total
Resistance in the Circuit
• Adding bulbs in series increases the
resistance.
• Adding bulbs in parallel decrease the
resistance.
Resistors in Combination
• Resistors in Series
R = R1 + R2
• Resistors in Parallel
1 1 1
 
R R1 R2
For a given battery:
• The current is the circuit is not always the
same.
• More resistance in the circuit, less current
in the circuit.
• Less resistance in the circuit, more current
in the circuit
• What stays the SAME about the battery is
its “the strength of its push”.
VOLTAGE,CURRENT AND
RESISTANCE
Voltage is the word we use for the “strength of
the push”
V=IR
If Voltage of the battery stays constant, and
the resistance of the circuit increases, the
current must decrease.