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