The motor effect can happen when you put a current-carrying wire in a magnetic field.
A current in a magnetic field experiences a force
When a a current-carrying wire, or any other conductor, is put between magnetic poles, the magnetic field around the wire interacts with the magnetic field it has been placed in.
This causes the magnet and the conductor to exert a force on each other.
To experience the full force, the wire has to be at 90 to the magnetic field.
If the wire runs parallel to the magnetic field, it won’t experience any force at all.
At angles in between, it’ll feel some force.
A good way of showing the direction of the force is to apply a current to a set of rails inside a horseshoe magnet.
A bar is placed on the rails, which completes the circuit.
This generates a force that rolls the bar along the rails
You can find the size of the force
The force acting on a conductor in a magnetic field depends on three things
The magnetic flux density-how many field(flux) lines there are in a region.
The size of the current through the conductor
The length of the conductor that’s in the magnetic field
When the current is at 90 to the magnetic field it is in, the force acting on it can be found using the equation:
F=BI1 Force=Magnetic flux density x current x length
\
A current-carrying coil of wire rotates in a magnetic field
The diagram below shows a basic dc motor.
Forces act on the side arms of a coil of wire that’s carrying a current.
Because the coil is on a spindle and the forces act one up and one down, it rotates
The split-ring commutator is a clever way of swapping the contacts every half turn to keep the motor rotating in the same direction
The direction of the motor can be reversed either by swapping the polarity of the dc supply (reversing the current) or swapping the magnetic poles over (reversing the field).
\
You can use Fleming’s left-hand rule to work out which way the coil will turn
·Loudspeakers work because of the motor effect
\
\
\
\
\
\