Electric motors

Question 1

Find direction of force

Answer 1

Fleming’s left-hand side
1) with left hand, point first finger = direction of the magnetic field
2) second finger = direction of current
3) thumb = direction of motion/force

Question 2

What does Fleming’s left-hand rule show ?

Answer 2

either current or the magnetic field is reversed, then the direction of the force will also be reversed

This can be used for all sorts of things = like motors

Question 3

The diagram on the right shows a basic dc motor.
Steps 1-3

Answer 3

1) Forces act on the two side arms of a coil of wire that’s carrying a current
2) These forces are just the usual forces which act on any current in a magnetic field
3) because the coil is on a spindle and the forces act one up and one down, it rotates.

Question 4

Steps 4-7

Answer 4

4) The split ring commutator is a clever way of swapping the contacts every half turn to keep the motor rotating in the same direction

5) the direction of the motor can be reversed either by swapping the polarity of the dc supply or swapping the magnetic poles over

6) The speed of the motor can be increased by increasing by increasing the current. Adding more turns to coil or increasing the magnetic flux density.

7) You can use Fleming’s left-hand rule to work out which way the coil will turn