Inside a battery, chemical reactions happen that produces a buildup of electrons. The electrons go to the negative end, while the positive end stays mostly empty. (These are called the negative and positive terminals. ) The longer this goes on, the larger the voltage between the two ends. When you connect a wire between the negative and positive ends, the electrons at the negative end suddenly have somewhere to go. They shoot toward the positive end, creating a current. The larger the voltage, the more electrons move to the positive end each second.

A resistor is anything in the circuit that adds resistance. You can buy an actual “resistor” at an electronics store, but in a circuits problem it might represent a light bulb or anything else with resistance.

Current = voltage divided by resistance This is usually written: I = V / R Think about what happens when you increase V (voltage) or R (resistance). Does this match what you learned in the explanations above?

The current is always the same at any point along the circuit. [3] X Research source When calculating voltage, it doesn’t matter where the resistor is on the circuit. You can pick up the resistors and move them around, and you’ll still have the same voltage across each one. We’ll use an example circuit with three resistors in series: R1, R2, and R3. This is powered by a 12 volt battery. We’ll find the voltage across each one.

For example, the three resistors R1, R2, and R3 have resistances of 2 Ω (ohms), 3 Ω, and 5 Ω respectively. The total resistance is 2 + 3 + 5 = 10 ohms.

Ohm’s Law says that the current I = V / R. The voltage across the whole circuit is 12 volts, and the total resistance is 10 ohms. The answer is I = 12 / 10 = 1. 2 amperes.

I = V / R IR = VR / R IR = V V = IR

Voltage across R1 = V1 = (1. 2A)(2Ω) = 2. 4 volts. Voltage across R2 = V2 = (1. 2A)(3Ω) = 3. 6 volts. Voltage across R3 = V3 = (1. 2A)(5Ω) = 6. 0 volts.

In our example, 2. 4 + 3. 6 + 6. 0 = 12 volts, the voltage across the whole circuit. If your answer is slightly off (for instance, 11. 97 instead of 12), you probably rounded a number at some point. Your answer is still correct. Remember, voltage measures the differences in charge, or numbers of electrons. Imagine counting the number of new electrons you see as you travel along the circuit. If you count them correctly, you’re going to end up with the total change in electrons from the beginning to the end.

You can have any number of wires in a parallel circuit. These instructions will still work for a circuit that splits into one hundred wires and comes back together.

Remember that adding voltage drops in a series circuit always results in the total voltage across the circuit. Think of each path the current takes as a series circuit. The same holds true for this: if you count up all the voltage drops, you’ll end up with the total voltage. Since the current through each of the two wires only passes through one resistor, the voltage across that resistor must equal the total voltage.

In mathematical terms: Itotal = I1 + I2 + I3. . . If you’re having trouble understanding this, imagine a water pipe split into two paths. The total amount of water flow is just the amount of water flow in each pipe, added together.

1 / Rtotal = 1 / R1 + 1 / R2 + 1 / R3 . . . For example, a circuit has a 2 ohm and a 4 ohm resistor in parallel. 1 / Rtotal = 1/2 + 1/4 = 3/4 → 1 = (3/4)Rtotal → Rtotal = 1/(3/4) = 4/3 = ~1. 33 ohms.

A circuit has 5 amperes of current running through it. The total resistance is 1. 33 ohms. According to Ohm’s Law, I = V / R, therefore V = IR V = (5A)(1. 33Ω) = 6. 65 volts.