How real electric motors work

John Storey


Note: These pages are intended to be read in conjunction with Joe's "Electric motors and generators" pages of the HSC Physics resources. Read those pages first. Once you've got the basic idea and understand the physical principles and the maths, you're ready to explore how real-life engineers have put physics into action to make our lives easier.

When it comes down to it, all these motor are using the same basic principle. In some cases, it’s easiest to think in terms of the force on a current-carrying wire in a static magnetic field. In other cases it’s easiest to think about two magnets (at least one of which is an electromagnet) attempting to align their poles north-to-south and south-to-north. However, both these explanations amount to the same thing, as James Clerk Maxwell so elegantly described with his four equations that form the basis of electromagnetism.

If you're tempted to pull a motor apart yourself, please think carefully about the risks involved before reaching for the tool kit. Some of the more important risks are listed at the end of this article. Also see Richard's page on Faraday's Law which contains an activity on "Building a motor and electrical generator".

Click on any picture for a high-resolution image. All pictures may be freely reproduced for educational purposes provided they are appropriately acknowledged.

You can download this entire document as a 2.3 MB PDF file , or read individual sections by following the links.

  1. “Universal” motors
  2. Advanced AC motors
  3. The infamous “ball-bearing” motor



Home |Physics Main Page |Faculty of Science | UNSW Main Page]  
Site Comments:
© School of Physics - UNSW 2006