Motors P3

In the exam you need to be able :

  • to explain how the motor effect is used in simple devices.

(Let me know if you can't read some of the tags on the pictures)

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  • Created by: Alice
  • Created on: 11-03-10 10:00

Fleming's Left-hand Rule

For the maximum force, the current and magnetic field are at right angles, and the motion is at right angles as well. This is summed up in Fleming's Left Hand Rule:

ThuMb = Motion

First Finger = Field

SeCond Finger = Current


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The Simple Electric Motor

The electric motor uses the interaction of a magnetic field on a current to produce a force. This is true from the smallest toy motor to a large traction motor.

The main parts of the motor are:

  • the magnets that provide the magnetic field. In this motor they are permanent magnets, but in many motors they are electromagnets.

  • the armature, which is a coil of wire free to turn. The armature in this motor is made of a single coil of wire. It has two poles.

  • The commutator, which connects the armature to the brushes. The current passes to the armature by the commutator.

  • The brushes that bring the current to the commutator.

When the current is turned on, the force from the current and the magnetic field makes the left hand side of the armature go up, while the right hand side goes down. The motor turns clockwise.

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The Simple Electric Motor (2)

The force which a simple motor can produce can be increased by:

  • increasing the current through the armature;

  • increasing the number of turns in the coils on the armature;

  • increasing the magnetic field strength. In a motor where the magnetic field strength is provided by electromagnets, the magnetic field strength can be changed quite easily.

This is a common problem with two pole motors, which have a single coil of wire.

Often a two pole motor needs a spin to get it going. Most toy motors have three poles. Therefore they can start whatever position the poles are. Larger motors have many more.

Electric motors can be made more efficient by having more poles, and circular magnets, which means that the magnetic field remains at 90 degrees all the time.

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The Motor Effect (experiment)


The carbon rod is NOT magnetic.

When no current flows, the rod is stationary

When we turn on the current, the rod experiences a force that makes it move

The direction of the force is determined by Fleming's Left Hand Rule

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A motor


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In the exam you need to know that:

When a conductor carrying an electric current is placed in a magnetic field, it may experience a force.

  • The size of the force can be increased by:

- increasing the strength of the magnetic field

- increasing the size of the current.

  • The conductor will not experience a force if it is parallel to the magnetic field.

  • The direction of the force is reversed if either the direction of the current or the direction of the magnetic field is reversed.

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this is useful :) thank you




Can I ask you a quick question. Well basically, my teacher gave me a question and I'm really stuck on it. 'state the two ways the force can be made to act in the opposite direction.' but on the revision card you said that the motor Turns clockwise, so if the force is made in the opposite direction will this mean that the motor will turn anticlockwise? Thanks. Btw brilliant revision cards- did help:)

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