Electric motors are inside many of the appliances we use every day, like hair dryers, washers, and fans. But how do they actually work? Do they make noise? The answer lies in the motor effect. This is when a wire carrying electricity interacts with a magnetic field, creating a force that can be used to power all sorts of things. Want to know more? Keep reading to learn about the motor effect and how it works.

Definition of the motor effect

Did you know that a current-carrying wire placed near a horseshoe magnet will actually deflect? How does this happen? It's due to the motor effect, which is when the electricity in the wire interacts with the magnetic field of the magnet to create a force. This magnetic force is what makes electric motors work, hence the name 'motor effect'. In short, the motor effect is when a current-carrying wire experiences a force in the presence of an external magnetic field. Keep reading to learn more about this fascinating phenomenon!

Causes of the motor effect

The basis of the motor effect is the fact that an electric current flowing through a wire produces a magnetic field.

Cause of the motor effect

Remember how a current-carrying wire has a magnetic field around it in a cylindrical shape, as explained in the article 'Electric Fields of Electric Currents'? Well, if you place this wire inside an external magnetic field, the cylindrical magnetic field of the wire will interact with the external magnetic field. This interaction is what creates a force on the wire, similar to the force between two bar magnets due to their magnetic fields interacting. So when we talk about the motor effect, we're referring to this force generated on the current-carrying wire due to its magnetic field interacting with an external magnetic field. Keep reading to dive deeper into the motor effect!

Direction of the force

If you want to determine the direction of the force in the motor effect, you can use Fleming's left-hand rule. This rule helps you figure out the direction of the force if you know the direction of the current and the external magnetic field involved. Simply hold your left hand in a certain way, and your thumb will indicate the direction of the force, your index finger will indicate the direction of the external magnetic field, and your middle finger will indicate the direction of the current. As a result, you'll see that the direction of the force is always perpendicular to the plane in which both the magnetic field and the current lie. This is a useful tool for understanding and predicting the behavior of electric motors and other devices that rely on the motor effect. Let's explore more about the motor effect and its applications!

Practice using Fleming's left-hand rule until you get correct answers to questions regarding the direction of the quantities in the motor effect consistently.

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If a current is running from south to north, and the magnetic field lines (from the magnetic field that the wire is in) run from west to east, then the force on the wire is downwards. Check this with Fleming's left-hand rule!

Formula of the motor effect

To determine the magnitude of the force on the wire in this scenario, we can use the motor effect formula:

F = BIL

where F is the force on the wire in newtons, B is the magnetic field strength in teslas, I is the current through the wire in amperes, and L is the length of the wire in meters that is in the external magnetic field.

In this case, we have:

B = 0.8 T (given)
I = 5 A (given)
L = 0.3 m (given)

Since the wire is perpendicular to the magnetic field lines, we can use the formula as is, without any adjustments:

F = (0.8 T) x (5 A) x (0.3 m) = 1.2 N

Therefore, the force on the wire is 1.2 newtons.

Diagram of the motor effect

Below is a nice diagram of the motor effect, where the horseshoe magnet's north pole is red and its south pole is green. The diagram shows the direction of the force as a result of the direction of the magnetic field and the current.

Motor effect experiment(s)

The simplest experiment you can do to demonstrate the motor effect is to get a horseshoe magnet and a wire that can carry a current. If you position the wire between the two poles of the horseshoe magnet, and drive a current through the wire, the motor effect will create a force on the wire, and the wire will deflect (if the force is big enough to overcome the weight and the friction of the wire).

Another experiment is one involving a battery, a small disc magnet, and some conducting wire. The setup is shown in the figure below: we place the magnet under the battery, and we bend and position the wire as shown. The magnetic field lines will go up and outwards from the magnet, so the magnetic field will be in opposite directions on both sides of the wire. The current will be from top to bottom (because the positive battery terminal is at the top), so the current will be downwards everywhere in the vertical parts of the wire. This causes the magnetic force generated on the wire to be opposite on either side, so the wire will start spinning around the battery.

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These are all great takeaways about the motor effect! It's important to note that the motor effect is a fundamental principle in electromagnetism, and it has countless applications in everyday life. From electric motors and generators to MRI machines and particle accelerators, the motor effect plays a crucial role in the functioning of many modern technologies.

Understanding the motor effect can also help us understand other related concepts, such as electromagnetic induction and Faraday's law, which are essential to the design and operation of many electrical devices.

Overall, the motor effect is a fascinating and important phenomenon that is worth exploring further for anyone interested in physics or engineering.

Motor Effect

What is the motor effect?

The motor effect is the magnetic force on a current-carrying wire in a magnetic field. 

How does the motor effect work?

The motor effect works through the magnetic force acting on the individual moving charged particles in the current-carrying wire.

What is the motor effect's formula?

The formula describing the size of the force of the motor effect is F=BIlsin(θ ), where F is the force, B is the magnetic field strength, I is the current through the wire, l is the length of the wire that is in the magnetic field, and θ  is the angle between the wire and the magnetic field lines.

How can the motor effect be demonstrated?

The motor effect can be demonstrated by putting a current-carrying wire between the poles of a horseshoe magnet. The wire should experience a force, which will deflect it a little bit.

Why does the motor effect happen?

The motor effect happens because there are charged particles in the current-carrying wire, and those charged particles experience a magnetic force in the magnetic field. The charged particles push the whole wire in the direction of that force.

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