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Before you can calculate the voltage of the resistor, you must first determine what type of circuit you are using. If you need to review the basics or need a little help understanding electrical circuits better, start with the first part. If not, skip it and go to the section about the type of circuit you need to deal with.
Steps
Understanding electrical circuits
- In a battery, a chemical reaction takes place and electrons are accumulated. These electrons go towards the negative end, while the positive end remains in a near-empty state (They are called cathode and anode). The longer this process takes, the greater the voltage between the two ends.
- When wiring between the cathode and anode, suddenly, the electron at the cathode has room to go. They shoot towards the anode, creating an electric current. The higher the voltage, the more electrons move towards the anode per second.
- A resistor is anything that belongs to a circuit and adds resistance to the circuit. You can buy a real “resistor” at an electrical store, but in circuit problems, resistance is usually represented by a light bulb or any other resistive object.
- Amperage = voltage divided by resistance
- It is usually written as: I = ^{V} / _{R}
- Think about what happens when V (voltage) or R (resistance) is increased. Does it match what you learned in the explanation above?
Calculate the voltage of the resistor (series circuit)
- The current is always the same at every point in the circuit. ^{[2] X Research Source}
- When calculating voltage, the position of the resistor in the circuit does not matter. You can take and change the resistor position, the voltage of each resistor will remain the same.
- Consider the example circuit with three resistors in series: R _{1} , R _{2} , and R _{3} . This circuit is powered by a 12V battery. We will find the voltage of each resistor.
- For example, the three resistors R _{1} , R _{2} , and R _{3} have resistances of 2 Ω (ohm), 3 , and 5 Ω respectively. The total resistance of the circuit is 2 + 3 + 5 = 10 ohms.
- Ohm’s law says that amperage I = ^{V} / _{R} . The voltage across the circuit is 12 volts, and the total resistance is 10 ohms. The answer is I = ^{12} / _{10} = 1.2 amp .
- I = ^{V} / _{R}
- IR = ^{V} R / _{R}
- IR = V
- V = IR
- Voltage of R _{1} = V _{1} = ( 1.2A )( 2Ω ) = 2.4V.
- Voltage of R _{2} = V _{2} = ( 1.2A )( 3Ω ) = 3.6V.
- Voltage of R _{3} = V _{3} = ( 1.2A )( 5Ω ) = 6.0V.
- In our example: 2.4 + 3.6 + 6.0 = 12V, which is the total voltage of the circuit.
- If the sum of the voltages is slightly lower (such as 11.97 instead of 12), you’ve probably rounded the number somewhere. Your answer is still correct.
- Remember that voltage measures the difference in charge, or number of electrons. Imagine you are counting the number of electrons you see as you move along a circuit. If you count correctly, you will eventually get the total charge present in the electrons from start to finish.
Calculate the voltage of the resistor (parallel circuit)
- Parallel circuits can have an arbitrary number of wires. This instruction still holds true for circuits that are divided into a hundred wires and then reassembled.
- Remember that in series circuits, the total voltage of the circuit is always equal to the sum of the voltages of each voltage drop.
- Think of each line path as a series circuit. The same holds true: when you add up the voltages of the whole resistor, you will eventually get the full circuit voltage.
- Since current flows through each wire through only one resistor, the voltage of that resistor must be equal to the total voltage.
- In mathematical terms: I _{sum} = I _{1} + I _{2} + I _{3} …
- If it’s confusing, imagine a water pipe split in two. Total water flow is simply the amount of water flowing through each pipe added together.
- ^{1} / _{R }_{sum} = ^{1} / _{R }_{1} + ^{1} / _{R }_{2} + ^{1} / _{R }_{3} …
- Take for example a circuit with 2 ohm and 4 ohm resistors installed in parallel. ^{1} / _{R }_{sum} = 1/2 + 1/4 = 3/4 → 1 = (3/4)R _{total} → R _{sum} = 1/(3/4) = 4/3 = ~1.33 ohms.
- Consider a circuit with a current of 5 amps flowing through it. The total resistance of the circuit is 1.33 ohms.
- According to Ohm’s law, we have: I = V / R, hence: V = IR.
- V = (5A)(1.33Ω) = 6.65V.
Advice
- If you have a complex circuit with series and parallel resistors, choose two that are close together. Find their combined resistance using the appropriate series or parallel resistance rule. Now you can think of them as a single resistor. Do this until you get a simple circuit with resistors either in parallel, or in series. ^{[7] X Research Sources}
- The voltage of a resistor is often called a “drop in voltage”.
- Understand the term:
- Circuit – consists of electrical circuit components (such as resistors, capacitors and inductors) that are connected by wires and where current can flow
- Resistor – part that can reduce or hinder current
- Amperage – the flow of charge entering the wire, unit: Amp, A
- Voltage – work done to move a charged particle; Unit: Volt, V
- Resistance of an object – measures its resistance to electric current; Unit: Hugs,
wikiHow is a “wiki” site, which means that many of the articles here are written by multiple authors. To create this article, volunteer authors have edited and improved the article over time.
This article has been viewed 68,936 times.
Before you can calculate the voltage of the resistor, you must first determine what type of circuit you are using. If you need to review the basics or need a little help understanding electrical circuits better, start with the first part. If not, skip it and go to the section about the type of circuit you need to deal with.
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