Lecture Nine Physics 100 Fall 2012

Review of Labs on Series and Parallel Circuits

We call a flow of charged particles current.

Electric CurrentElectric current (or just current) is the rate at which

charges (electrons) flow through a wire.

More generally, current 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

Bulbs present an obstacle

(or resistance) to the flow of current.

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 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.