How To Find Voltage Across A Resistor

Download Article

Download Commodity

Earlier you tin can calculate the voltage across a resistor, you'll first have to determine what kind of circuit you are using. If you need a review of the basic terms or a little assist agreement circuits, start with the offset section. Otherwise, bound ahead to the blazon of circuit yous have to solve.

ane

Learn about electric current. Let'due south retrieve nigh current by using an analogy: imagine yous pour a bag of corn kernels into a basin. Each corn kernel is an electron, and the stream of kernels flowing into the basin is the current.^[1] When talking nigh the flow, you depict information technology by saying how many kernels are flowing each second. When talking about a electric current, y'all measure out information technology in amperes (amps), or a sure (very big) number of electrons flowing per second.
2

Call up nigh electric charge. Electrons take a "negative" electrical accuse. This means they attract (or menses toward) objects with a positive accuse, and repel (or flow away from) objects with a negative accuse. Since they're all negative, electrons are always trying to push button away from other electrons, spreading out wherever they can.

Ad
3
Understand voltage. Voltage measures the difference in electrical accuse between two points. The greater the difference, the more than energetically the two sides attract each other. Hither'due south an example with an everyday battery:
- 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 chosen the negative and positive terminals.) The longer this goes on, the larger the voltage between the ii ends.
- When yous connect a wire between the negative and positive ends, the electrons at the negative end all of a sudden accept somewhere to become. They shoot toward the positive stop, creating a electric current. The larger the voltage, the more electrons motility to the positive stop each second.
4
Figure out resistance. Resistance is exactly what it sounds like. The more resistance something has, the harder it is for the electrons to push through. This slows the current, since fewer electrons tin can push button through each second.
- A resistor is anything in the circuit that adds resistance. You can buy an bodily "resistor" at an electronics store, but in a circuits trouble it might represent a light bulb or anything else with resistance.
5
Memorize Ohm's Law. At that place'south a very elementary relationship betwixt current, voltage, and resistance. Write this down or memorize it; yous'll utilize it often when solving circuit issues:
- Electric current = voltage divided by resistance
- This is usually written: I = ^Five / _R
- Retrieve about what happens when y'all increase V (voltage) or R (resistance). Does this match what you learned in the explanations higher up?
Advertisement

1
Understand a series circuit. A series excursion is easy to identify. It'due south just one loop of wire, with everything arranged in a row. The current flows effectually the entire loop, going through each resistor or element in order.
- The electric current is always the same at whatever signal along the excursion.^[two]
- When calculating voltage, information technology doesn't matter where the resistor is on the excursion. You lot can pick up the resistors and move them around, and you'll still accept the same voltage across each 1.
- We'll use an instance circuit with three resistors in serial: R₁, R₂, and R₃. This is powered by a 12 volt bombardment. We'll detect the voltage across each one.
two
Summate the total resistance. Add all resistance values on the circuit. The respond is the full resistance of the series excursion.
- For case, the three resistors R_one, R_ii, and R_three have resistances of 2 Ω (ohms), 3 Ω, and 5 Ω respectively. The total resistance is 2 + three + 5 = ten ohms.
3
Find the current. Use Ohm's Law to find the current of the unabridged circuit. Call back, the current is the same anywhere on a series circuit. Once we calculate the electric current this way, we can use it for all our calculations.
- Ohm's Law says that the current I = ^V / _R. The voltage across the whole circuit is 12 volts, and the full resistance is 10 ohms. The answer is I = ¹² / _ten = 1.2 amperes.
iv
Adjust Ohm's Constabulary to solve for voltage. With basic algebra, nosotros can change Ohm's Law to solve for voltage instead of electric current:
- I = ^V / _R
- IR = ⁵R / _R
- IR = Five
- V = IR
5
Calculate the voltage across each resistor. Nosotros know the resistance, we know the electric current, and we have our equation. Plug in the numbers and solve. Here's our example trouble solved for all three resistors:
- Voltage across R₁ = 5_i = (1.2A)(2Ω) = 2.four volts.
- Voltage across R₂ = V_two = (i.2A)(3Ω) = 3.6 volts.
- Voltage across R_three = Five_iii = (1.2A)(5Ω) = half-dozen.0 volts.
6
Bank check your respond. In a series circuit, the sum of all your answers must equal the total voltage.^[3] Add together up every voltage you calculated and run into if y'all get the voltage of the entire circuit. If you didn't, get back and check for mistakes.
- In our example, 2.4 + 3.half-dozen + six.0 = 12 volts, the voltage beyond the whole circuit.
- If your reply is slightly off (for case, 11.97 instead of 12), yous probably rounded a number at some indicate. Your answer is still right.
- Retrieve, voltage measures the differences in accuse, or numbers of electrons. Imagine counting the number of new electrons you run into as you travel forth the excursion. If you count them correctly, you're going to end upwards with the total alter in electrons from the start to the end.
Ad

i
Understand parallel circuits. Imagine a wire leaving one stop of a battery, and then splitting into ii separate wires. These two wires run parallel to each other, then join up again before they reach the other end of the battery. If at that place's a resistor on the left wire and a resistor on the correct wire, those 2 resistors are continued "in parallel."^[4]
- You tin can have whatever number of wires in a parallel circuit. These instructions volition all the same work for a circuit that splits into one hundred wires and comes dorsum together.
ii

Call up well-nigh how the current flows. In a parallel circuit, the current flows beyond each path available to it. Electric current will catamenia through the wire on the left, cross the left resistor, and reach the other end. At the same fourth dimension, current will flow through the wire on the correct, cross the right resistor, and attain the end. No part of the current doubles back or flows through two parallel resistors.
3
Use the total voltage to detect the voltage across each resistor. If y'all know the voltage across the whole circuit, the respond is surprisingly easy. Each parallel wire has the same voltage every bit the entire circuit.^[5] Let's say a circuit with 2 parallel resistors is powered by a 6 volt battery. The voltage across the left resistor is six volts, and the voltage across the right resistor is 6 volts. Information technology doesn't even matter how much resistance there is. To understand why, recall back to the series circuits described higher up:
- Retrieve that adding voltage drops in a series circuit ever results in the total voltage across the excursion.
- Recall of each path the current takes as a series excursion. The same holds truthful for this: if yous count up all the voltage drops, you lot'll stop up with the total voltage.
- Since the electric current through each of the two wires simply passes through one resistor, the voltage beyond that resistor must equal the total voltage.
4
Summate the full current of the circuit. If the problem doesn't tell you what the total voltage of the circuit is, you'll need to complete a few more steps. Start past finding the total current passing through the circuit. In a parallel circuit, the full current is equal to the sum of the current running through each parallel path.^{[half dozen]}
- In mathematical terms: I_total = I_ane + I₂ + I₃...
- If you're having trouble agreement this, imagine a water pipage separate into two paths. The total amount of h2o flow is but the amount of water flow in each piping, added together.
5
Compute the total resistance of the excursion. Resistors are not as effective in a parallel circuit, because they only block the electric current going along ane wire. In fact, the more wires in that location are, the easier it is for the electric current to find a way through. To find the total resistance, solve for R_full in this equation:
- ⁱ / _{R_total} = ¹ / _{R_one} + ^one / _R₂ + ¹ / _R₃ ...
- For instance, a circuit has a two ohm and a 4 ohm resistor in parallel. ⁱ / _{R_total} = 1/two + 1/4 = three/4 → one = (three/4)R_total → R_total = ane/(three/four) = 4/iii = ~1.33 ohms.
six
Find the voltage from your answers. Retrieve, once we find the total voltage of the circuit, we have establish the voltage across any i of the parallel wires. Solve for the whole circuit using Ohm'due south law. Here's an example:
- A excursion has five amperes of electric current running through it. The full resistance is 1.33 ohms.
- According to Ohm's Law, I = V / R, therefore V = IR
- V = (5A)(1.33Ω) = six.65 volts.
Advertizing

Add together New Question

Question

What is the percentage of applied voltage that will be dropped across r3=seventy if r1=80 and r2=50?

Information technology would exist 35%. The higher the resistance, the higher the voltage drop. The ratio of resistances hither is 80:fifty:seventy. Solving for 70 ohms, we get 35%.
Question

What is the voltage of a threescore ohm resistor if the circuit voltage is 150 volts with 2 parallel 30 ohm resistors and 1 60 ohm resister in the series?

Bold yous intend to ask what is the voltage drop across the sixty ohm resistor, the answer is 120v. The two parallel 30 ohm resistors accept an equivalent resistance of 15 ohms. 1/(1/xxx + 1/thirty) = 15. The full resistance appears as 75 ohms to the 150v source. Notice the circuit current past I = E/R or I = 150/75 = ii amps. Find the voltage drop for the 60 ohm resistor with E = I x R or E = 2 x 60 = 120V drop across the 60 Ohm resistor.
Question

What becomes the Voltage if we use 2 resistors of 4W in parallel?

As any other data is non provided, the voltage beyond two resistors of 4w in parallel is the same.
Question

A excursion has three resistors continued in a series. The resistance of resistor R2 is 220R, and it has a voltage drop of 44V. How do I summate the current flow through resistor R3?

Upnorth Here

Top Answerer

The current in whatever part of a series circuit is the aforementioned everywhere.
Question

How do I go the voltage driblet?

You calculate the voltage drop over a component in a circuit past finding the current and resistance running through and exerted upon the component before multiplying them together.
Question

How do I calculate the voltage across a resistor in series when I know the voltage across i resistor and total voltage from bombardment?

Upnorth Here

Top Answerer

You know the resistance and the current (which is the same anywhere in a series circuit). The voltage driblet for each resistor is E(ten) = I x R(ten) for each resistor (x), i.due east., R(ane), R(2), R(iii).
Question

How do I figure out what resistor I need if I know the voltage and current?

Upnorth Here

Top Answerer

Yous take the basic formula of East = I 10 R, solve for R -> R = East / I. In other words, accept the required voltage drib (in volts) and divide by the current (in amps) in the resistor and determine the resistance (R) in ohms.
Question

How practise I find the voltage to any resistor in a series parallel network?

Upnorth Here

Top Answerer

Y'all find the resistance of the serial portion past calculation together the resistances. You then detect the resistance of the parallel portions with the formula shown above: i / Rtotal = 1 / R1 + i / R2 + one / R3... If the series resistances are in series with the parallel, you lot add them together with the calculated parallel resistance. If the series resistances are in parallel with others, they become one of the resistances, "R1", of the parallel formula for calculating their contribution to the resistance of the entire circuit.
Question

How can I decide voltage drop given the resistance and voltage?

Upnorth Hither

Peak Answerer

The voltage drop is already known, if all you have is a resistance and a known voltage. The current tin can be adamant by dividing the voltage by the resistance, if that'southward what you're asking.
Question

How tin I decide the voltage if I know the ii batteries that are connected in series?

Upnorth Here

Pinnacle Answerer

The voltage of the combination of multiple cells (batteries) in series is the sum of the voltage of all the cells. Two 9-volt batteries in series would requite you 18 volts.

Show more answers

Inquire a Question

200 characters left

Include your email address to get a message when this question is answered.

Submit

Advertising

Video

The voltage across a resistor is oftentimes chosen a "voltage drop."
If you have a complicated circuit that involves resistors in serial and resistors in parallel, pick two nearby resistors. Find the total resistance across them using the rules for resistors in parallel or in series, as appropriate. Now you lot tin can care for them every bit a unmarried resistor. Go on doing this until you lot have a unproblematic circuit with resistors either in parallel or in serial.^[7]
Understand the terminology:
- Excursion – composed of elements (e.g. resistors, capacitors, and inductors) connected by wires and wherein current tin pass through
- Resistors – elements that can reduce or resist current
- Current – menstruation of charge into wires; unit: Ampere, A
- Voltage – work done per unit charge; unit: Voltage, V
- Resistance – measurement of the opposition of an element to electric current; unit: Ohm, Ω

Thanks for submitting a tip for review!

Virtually This Article

Article Summary 10

To calculate voltage across a resistor in a serial excursion, outset by adding together all of the resistance values in the circuit. Then, split up the voltage beyond the excursion past the total resistance to find the current. Once you lot accept the electric current, calculate voltage for the private resistors past multiplying the current by the resistance. For example, in a series circuit with 3 resistors of 2, 3 and v Ohms, and a voltage of 12 volts, the current would be 12 divided past 10, or 1.2 amperes. For the 2 Ohm resistor, the voltage would exist 1.2 times 2, or 2.4 volts. If you want to learn how to calculate voltage in a parallel circuit, go along reading the article!

Did this summary aid you?

Thank you to all authors for creating a page that has been read 817,452 times.