What is Electric Current? - Definition, Unit & Types

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  • 0:05 The Flow of Electrons
  • 2:31 Direct and Alternating Current
  • 5:37 Units of Current
  • 6:30 Lesson Summary
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Lesson Transcript
Instructor
Jim Heald

Jim has taught undergraduate engineering courses and has a master's degree in mechanical engineering.

Expert Contributor
Christianlly Cena

Christianlly has taught college physics and facilitated laboratory courses. He has a master's degree in Physics and is pursuing his doctorate study.

Like a river current is the flow of water molecules, electrical current is the flow of charged particles. In this lesson, we're going to explore what electrical current is, what causes it, and that, unlike a water current, electrical current doesn't always flow in one direction.

The Flow of Electrons

When you hear the word 'current,' what does it make you think of? Perhaps water flowing down a river? That's a good association, because that's precisely the reason electrical current was given its name. Electrical current is very similar to a water current, only instead of water molecules moving down a river, charged particles move down a conductor. In this lesson, we're going to explore what exactly current is, what causes it, and find out that, unlike a water current, electrical current doesn't always flow in one direction.

Current is the flow of charged particles through a conducting medium, such as a wire. When we talk about electricity, the charged particles we're referring to are almost always electrons. You see, the atoms in a conducting material have lots of free electrons that float around from atom to atom and everywhere in between. The motion of these electrons is random, so there is no flow in any given direction. However, when we apply a voltage to the conductor, all of the free electrons will move in the same direction, creating a current.

A curious thing about electric current is that while the electrical energy transfers through the conductor at nearly the speed of light, the electrons themselves move much, much slower. In fact, if you were to walk leisurely alongside a current carrying wire, you would be traveling more than 100 times faster than the electrons!

Electrons move slowly because they do not move very far to transfer energy to each other.
Why Electrons Move Slowly

To see why this is, we can visualize a current carrying wire like a tube filled with marbles. The marbles represent the electrons and the tube represents the wire. If we put a marble into one end of the tube, it pushes on the first marble, which pushes on the next marble, and so on down the line. If we were standing at the other end of the tube, we would see a marble exit at the same time the other marble entered. In other words, the motion, and therefore the energy, was transmitted nearly instantaneously. However, each individual marble only moved a tiny distance in the tube to transfer that energy. Because the electrons in a wire don't have to travel very far to transfer their energy to the next electron, their overall progress through the wire is relatively slow.

Direct and Alternating Current

There are two different types of current in widespread use today. They are direct current, abbreviated DC, and alternating current, abbreviated AC. In a direct current, the electrons flow in one direction. Batteries create a direct current because the electrons always flow from the 'negative' side to the 'positive' side.

In a direct current, the electrons travel in one direction.
Direct Current Image

Alternating current, abbreviated AC, pushes the electrons back and forth, changing the direction of the flow several times per second. In the United States, the current changes direction at a rate of 60 hertz, or 60 times in one second. The generators used in power plants to produce electricity for your home are designed to produce alternating current. You've probably never noticed the lights in your house actually flicker as the current changes direction because it happens too fast for our eyes to detect.

So, why do we need two types of current, and which one is better? Well, that's a good question, and the fact that we're still using both types of current should tell you that they both serve a purpose. Back in the 19th century, it was understood that to send power efficiently over the long distance between a power plant and a home, it had to be transmitted at a very high voltage. The problem was that sending really high voltage into a home was extremely dangerous for the people living there.

The solution to this problem was to reduce the voltage right outside the home before sending it inside. With the technology that existed at the time, it was much easier to reduce the voltage of AC than it was of DC, so AC won out as the preferred type of current. To this day, we still use AC for all of our long-distance power transmission, largely because of its ability to easily transform to other voltages.

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Additional Activities

Electric Current True or False Activity

In this activity, you will check your knowledge regarding the definition, unit, and types of electric current presented in the lesson.

Directions

Determine whether the following statements are true or false. To do this, print or copy this page on a blank paper and underline or round the answer.

1. Free electrons are the electrons that are not attached to the nucleus of an atom and are free to move when external energy is applied.

True | False

2. Batteries create a direct current because the electrons flow from the positive to the negative side.

True | False

3. The standard rate at which alternating current reverses direction is at 60 Hz.

True | False

4. Any material having free charged particles that easily flow is called an insulator.

True | False

5. AC is used primarily for long-distance power transmission, largely because of its ability to easily transform into other voltages.

True | False

6. The rate of electrical flow is measured in amperes.

True | False

7. As voltage is applied in a wire, all of its free electrons will move in the same direction.

True | False

8. A generator produces a direct current through the conversion of mechanical energy into electrical energy.

True | False

9. The speed of electrons as they drift through a conducting wire is surprisingly fast.

True | False

10. An electric current is said to exist when there is a net flow of electric charge through a region.

True | False


Answer Key

1. True

2. False, because the correct statement is, Batteries create a direct current because the electrons flow from the negative to the positive side.

3. True

4. False, because the correct statement is, Any material having free charged particles that easily flow is called a conductor..

5. True

6. True

7. True

8. False, because the correct statement is, A generator produces an alternating current through the conversion of mechanical energy into electrical energy.

9. False, because the correct statement is, The speed of electrons as they drift through a conducting wire is surprisingly slow.

10. True

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