# Circuit Theory Basics

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• 0:00 What is a Circuit?
• 0:48 Features of Circuits
• 2:26 AC vs. DC
• 3:06 What Do Circuits Do?
• 3:48 Lesson Summary
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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.

Learn what a circuit is, how to describe the features of circuits, and be able to differentiate between AC and DC circuits in everyday life. Complete a quiz to test your knowledge.

## What is a Circuit?

In modern life, circuits are everywhere. Without circuits, you wouldn't have indoor lights. Without circuits, you wouldn't have the computer you're using to watch this lesson. Without circuits, you wouldn't have anything that is powered by electricity.

A circuit is a series of electrical components or devices connected together in a complete loop, allowing electric current in the form of charged electrons to flow through it and power the components.

There are practically an unlimited number of types of components that could go into a circuit, including batteries, bulbs, resistors, inductors, switches, capacitors, buzzers, diodes, temperature controls called thermistors, light sensors, and many others.

## Features of Circuits

There are certain features of a circuit that can be measured, which can be useful to make sure circuits operate correctly, and to troubleshoot when things go wrong. Current is the rate of flow of charge in a circuit, measured in amps. In other words, it is the amount of charge that passes through a point in a circuit per second. The faster the current is flowing, the more electrical energy is being brought to the components in that circuit.

Another feature is called resistance. Resistance is how much the components in a circuit hold back the flow of charge going through them, measured in ohms. A large resistance means less current will flow.

Probably the hardest feature to understand is voltage, otherwise known as potential difference. This is a difference in a number called potential between each side of a component in a circuit, measured in volts. But what does this mean?

Well, let's imagine that a circuit is a water slide. Instead of flow current, we have the flow of water. Water goes down the slide to power the components. The current is the amount of water that flows per second. The battery is like the water pump that sends the water back up to the top. In this analogy, the potential difference is the difference in height between the top of the water slide and the bottom. It represents how downhill the circuit is. Larger potential differences, just like larger current measurements, lead to more power being transmitted. And last of all, resistance is how wide the water slide is. A wider tunnel allows water to flow more quickly and easily.

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