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ZingPath: Electromagnetic Force and Induction

Designing an Electric Motor

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Electromagnetic Force and Induction

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Lesson Focus

Designing an Electric Motor

Physics

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Learners will observe how different parts of an electric motor affect the motor’s rotation, and build motors to compete in a series of races.

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Now You Know

After completing this tutorial, you will be able to complete the following:

  • Identify the parts of a basic electric motor.
  • Describe the effect of battery voltage on the rotation of an electric motor.
  • Describe the effect of magnet strength on the rotation of an electric motor.
  • Describe the effect of the number of loops in the coil on the rotation of an electric motor.
  • Describe changes that can be made to parts of an electric motor that will affect the direction of rotation of the motor.

Everything You'll Have Covered

Electric motors transform electrical energy into mechanical energy. In a basic electric motor, a battery is connected to a coil. As electric current flows through the coil, the coil acts as an electromagnet. That is to say that the flow of electricity through the conductive wire of the coil generates a magnetic field. This is one of two magnetic fields involved in the rotation of the motor. A second magnetic field exists due to the presence of a magnet that surrounds the coil.

Magnets have two poles, generally referred to as north and south. The north pole of one magnet and the south pole of a second magnet will attract each other by a magnetic force. Like poles, on the other hand, will repel each other. Thus, in the electric motor, one side of the coil will be attracted to the north pole, and repelled from the south pole of the magnet. The other side of the coil will be attracted to the south pole, and repelled from the north pole. This causes the coil to begin to rotate.

When the coil has rotated parallel to the magnetic field of the magnet, so that the sides of the coil are pointed directly at the poles of the magnet, a part called a commutator interrupts the flow of electrical current through the coil. Without the electrical current, the coil is no longer attracted to the magnet. The coil's angular momentum causes it to continue rotating. As it rotates past the point where it is parallel to the magnetic field, the flow of current through the coil resumes, but in the opposite direction. The side of the coil that was attracted to the north pole of the magnet is now attracted to the south pole. This allows for continuous rotation.

The rotational speed of a motor depends on the voltage of the battery, the size and strength of the magnet, and the number of loops of wire in the coil. Higher voltage batteries result in a greater current through the coil, which in turn generates a stronger magnetic field in the electromagnet. Including more loops of wire in the coil also increases the magnetic field in the electromagnet. A stronger or larger permanent magnet surrounding the coil exerts a greater magnetic force on the coil's magnetic field.

Tutorial Details

Approximate Time 20 Minutes
Pre-requisite Concepts electricity, energy, magnetism
Course Physics
Type of Tutorial Concept Development
Key Vocabulary current, electric, electricity