To keep the coil
rotating, the current must be reversed each time the coil has rotated
through 180°
The commutator does this.
You should be
able to use diagrams and/or other appropriate information to explain
how electromagnetic effects are used in simple d.c. motors and circuit
breakers.
NB
Details of the split ring commutator, for reversing the current to a
d.c. motor each half turn, will not be examined (from 1993 onwards!)
Here
is a link to a set of pages from Schoolscience - this takes you through
how the motor works with some interactive illustrations - worth a look!
(but remember the commutator is NOT on the syllabus anymore!)