Force on a Current-carrying Conductor & Motor Effect 

Reminder! Moving charges (electric currents) produce a magnetic field Conventional current – electrons flow in the opposite direction

Magnetic force on current We know that a current produces a magnetic field. It therefore makes sense that the current will be affected by placing a magnet nearby N S

Magnetic force on current Due to the magnetic field by the current the magnet will cause force on the wire. If there is not force holding the wire in place then the wire will move

Fleming’s left hand rule

Direction of force

Example FORCE S N MAGNETIC FORCE CURRENT

You try N 1. S

You try N 2. S

You try 3. S N WATCH IT IN ACTION!

Question Time! Magnetic fields Draw the magnetic field around: A straight wire b) a solenoid 2. What direction do magnetic field lines always point? 3. What happens to the magnetic field if the direction of the current is reversed? Fleming’s Left Hand Rule What happens to a wire carrying current when it is placed at right angles to a magnetic field? Draw a diagram showing the direction of current, magnetic field and movement. What angle are these all to each other?

The DC motor This uses a rectangular coil in a magnetic field. Use Fleming’s LHR to find the force on each part of the wire. Magnetic field direction On this side the force is down On this side the force is up

This makes the loop rotate... If the N and S poles are opposite, you get the opposite force.

Split ring commutators These make the current switch direction every half turn. This means the motor can keep spinning in one direction.