Electric Circuits Series and Parallel Circuits Making Electricity

Electric Circuits Series and Parallel Circuits Making Electricity Work for Us

Requirements for a Circuit • Electric Potential Source – battery – power supply – electrical outlet • Load – resistor – light bulb – appliances • Conductors – wires to connect – switches + -

Measuring Voltage and Current • Voltmeter – measures voltage – voltage across – wired in parallel • Ammeter – measures current – current through – wired in series V + + A - -

Series Circuit R 1 R 2 + R 3 V -

Simple Series Circuit • 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.

Series (continued) • 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. • RTOT = R 1 +R 2 +R 3 + …… + RN

Parallel Circuit + V R 1 - R 2 R 3

Parallel Circuit • 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.

Parallel (continued) • 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,

Complex Circuit R 1 R 3 + R 2 V - R 4

Simplifying Complex Circuits • 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.

Overloading Circuits • 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