6.15

What’s the motor effect?

"If there’s a magnetic field perpendicular to acurrent in a wire, the wire moves in a direction perpendicular to the field and the current" (FLHR)

So what about if we move a wire in a magnetic field?  What happens in the wire?

 When we move a wire in a magnetic field, a current is induced in the wire

 6.15 recall that a voltage is induced in a conductor or a coil when it moves through a magnetic field or when a magnetic field changes through it; also recall the factors which affect the size of the induced voltage

<<induction - magnet moving into coil (slow, fast, poles reversed).swf>>

6.15 Practical - model answers

·         

If you...

·         Push the North pole of the magnet into the coil

A negative current flow shown by a negative deflection on the ammeter

·         Keep the magnet stationary within the coil

No current

3.  Pull the North pole of the magnet out of the coil

A positive current

4.  Push the South pole of the magnet into the coil

A positive current

5.  Push the North pole of the magnet slowly into the coil

A smaller negative current  

6.  Push the North pole of the magnet quickly into the coil

A larger negative current  

7.  Change the coil for one with more turns of wire and push the North pole of the magnet into the coil

A larger negative current  

8.  Push the North pole of a neodymium (strong) magnet into the coil

A larger negative current

9.  Move the magnet in and out of the coil repeatedly.  What sort of current is this?

An alternating current

 

6.15 Plenary answers

·         Explain carefully how you can induce a current in a wire                (3 marks)

·         State 3 ways you can increase the size of this induced current (3 marks)

 

Answers

·         The wire must be perpendicular to a magnetic field

·         The wire and magnetic field must move relative to each other – the wire must "cut" through the magnetic field lines/lines of magnetic flux as it moves

·         A current is induced in the wire.  The induced current is perpendicular to both the field and the motion

 

·         Increase the strength of the magnets

·         Increase the speed of the relative motion

·         Use a coil of wire instead of a single piece of wire

 

induction - magnet moving into coil (slow, fast, poles reversed).swf Download this file

current induced in a moving wire_2.swf Download this file

current induced in a moving wire.swf Download this file