How to Find Equivalent Resistance

How to Find Equivalent Resistance
Coming up next: Electric Motors & Generators: Converting Between Electrical and Mechanical Energy

You're on a roll. Keep up the good work!

Take Quiz Watch Next Lesson
 Replay
Your next lesson will play in 10 seconds
  • 0:00 What Is Equivalent Resistance?
  • 0:47 Calculating Equivalent…
  • 1:32 Example Equations
  • 2:39 Lesson Summary
Save Save Save

Want to watch this again later?

Log in or sign up to add this lesson to a Custom Course.

Log in or Sign up

Timeline
Autoplay
Autoplay
Speed

Recommended Lessons and Courses for You

Lesson Transcript
Instructor: David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

After completing this lesson, you will be able to explain equivalent resistance and use equations to find the equivalent resistance of a basic series or parallel circuit.

What Is Equivalent Resistance?

Before we address what equivalent resistance is, we should first define resistance itself. Resistance is a measure of how much a component or material resists the flow of electricity through it, measured in ohms. It's inversely proportional to current: more resistance means less current will flow; less resistance means more current will flow.

Equivalent resistance may sound like a complex term, but it's really not. It's just a fancy way of saying total resistance. When you have a circuit with more than one component in it, we need to have a way of calculating the total effective resistance of the whole circuit or of one part of the circuit.

Calculating Equivalent Resistance

The way we calculate equivalent resistance depends on whether we're working with a series or a parallel circuit. A series circuit is one where all the components are connected in a single, continuous loop. A parallel circuit is one where the components are connected in separate branches. The method we use to calculate equivalent resistance is different for each type of circuit.

Series vs. Parallel Circuits

For a series circuit, we simply add up the resistances of each component. However, in a parallel circuit, the reciprocal of the total resistance is equal to the sums of the reciprocals of the resistances of each branch.

Equivalent Resistance for Series vs. Parallel

Let's go through an example of each type.

Example Equations

Let's say you have a series circuit containing a resistor, a bulb, and a battery. The resistor has a resistance of 6 ohms, and the bulb has a resistance of 3 ohms. What is the equivalent resistance of the circuit?

Simple: 6 + 3 = 9 ohms

Series Example
Series Example

But now if we connect those two components in a parallel circuit, our calculations get a little more complex. We can say that the reciprocal of the total resistance equals one over six, plus one over three.

To unlock this lesson you must be a Study.com Member.
Create your account

Register to view this lesson

Are you a student or a teacher?

Unlock Your Education

See for yourself why 30 million people use Study.com

Become a Study.com member and start learning now.
Become a Member  Back
What teachers are saying about Study.com
Try it risk-free for 30 days

Earning College Credit

Did you know… We have over 200 college courses that prepare you to earn credit by exam that is accepted by over 1,500 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.

To learn more, visit our Earning Credit Page

Transferring credit to the school of your choice

Not sure what college you want to attend yet? Study.com has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.

Create an account to start this course today
Try it risk-free for 30 days!
Create an account
Support