Can someone explain AC induction motors and the universal motor? (1 Viewer)

[ragingcurry]

How does the AC induction motor and the universal motor work?

I read PIF and Jacaranda and still don't understand

 

[leehuan]

Firstly, you need to be aware about why (according to Lenz's law) if you spin a magnet on top of something like an aluminium disk, that disk will rotate in the same direction as that of the magnet.

Then you can try to understand the AC induction motor. I personally didn't understand it myself until after trials, like 3 weeks before HSC it finally clicked

 

[leehuan]

When the magnetic rotates, there will be a induced current in the aluminium disc. By Lenz's Law, this current will act in such a way as to oppose the change in relative motion that caused it. The result of that the aluminium disc will appear to chase the spinning magnet.

The part you get stuck at is why the disc is following the magnet? Thinking in terms of relativity, by following the magnet you are decreasing the relative motion between the disc and the magnet. Thus by decreasing the relative motion you are essentially minimising this change (Lenz law) to stay stationary.

Whilst I perfectly agree with your explanation, this relativity word may accidentally cause someone to think about special relativity instead.