# 2009 Physics HSC Q7 (1 Viewer)

#### Jonothancroller

##### Member
http://imgur.com/vm1I8cD

Hey, so the answer is C but I really don't get how. Can someone show me the method to do this?

pm'd

#### pikachu975

##### I love trials
Moderator
Simple demonstration of an AC INDUCTION MOTOR:

The copper disc wants to oppose the change in flux (Lenz's Law) so the disc rotates in the same direction as the magnet because if it reaches the same speed, there would be no relative motion (i.e. no change in flux). It can't rotate in the opposite direction as that would increase change in flux.

##### New Member
Could you please also pm me the reasoning, I understand that C means no relative motion, but perhaps need a better way of thinking about it?

#### Fizzy_Cyst

##### Well-Known Member
Could you please also pm me the reasoning, I understand that C means no relative motion, but perhaps need a better way of thinking about it?
This is the very last concept in the Motors and Generators topic.

No school is up to it at this stage (Unless you do M&G first) and it is a application of Faraday/Lenz Laws in an AC induction motor.

If you acquire a solid understanding of Faraday/Lenz when you do it in school — this will be a breeze