1. Series and Parallel Circuits Making Electricity Work for Us

2.  Electric Potential Source ◦ battery ◦ power supply ◦ electrical outlet  Load ◦ resistor ◦ light bulb ◦ appliances  Conductors ◦ wires to connect ◦ switches + -

3. + - V A + -  Voltmeter ◦ measures voltage ◦ voltage across ◦ wired in parallel  Ammeter ◦ measures current ◦ current through ◦ wired in series

4.  Overloaded Circuit ◦ Wires connected in a short circuit ◦ Too many devices in parallel  Current becomes too high ◦ wires become too hot ◦ fire danger  Protection shuts off the power ◦ fuse burns out ◦ circuit breaker opens

5. A junction is an “intersection” or area of branching in a circuit. Junction Rule: The Current (amps) Rule The current flowing into a junction must equal the current going out of the junction. I in = I out

6. Around any complete loop in a circuit, the voltage gains (from the battery) must equal the voltage drops (through the bulbs). V gains = V drops

7. + - V R1R1 R2R2 R3R3

8.  Current has only one way to go through the resistors.  The current through each resistor is the same.  To get the total (or equivalent) resistance, add up the resistance of all the resistors.  The current of the circuit is equal to the supply voltage divided by the total resistance.

9.  The voltage drop across each resistor is equal to the current times the resistance (V = IR).  The total voltage drop across the resistors is equal to the voltage provided by the supply.  R TOT = R 1 +R 2 +R 3 + …… + R N

10. + - VR2R2 R3R3 R1R1

11.  The voltage is the same across each resistor.  The current splits between resistors. The current will like the easiest path (the least resistance), so there will be more current in the path of the smallest resistor.  The total current in the circuit equals the sum of the currents in the branches.  As the number of parallel branches increases, the overall resistance decreases.

12.  The equivalent resistance of two identical resistors in parallel is one half the value of the individual resistors.  For two resistors that are not the same,  For more than two resistors,

13. R2R2 R3R3 R4R4 + - V R1R1

14.  1. Find the parts of the circuit where resistors are simply in parallel or simply in series. In the circuit above, R 3 and R 4 are simply in series. There are no resistors simply in parallel.  2. If two or more resistors are in series, combine them in an equivalent resistance.  3. If two or more resistors are in parallel, combine them in an equivalent resistance.  4. Repeat steps 1 and 2 until the circuit has been simplified into a single resistance.  5. Determine the current of the simplest circuit.  6. Work back out, calculating the voltage across each resistor the current through each resistor using Ohm’s Law.