DC Motor

Question 1

To make dc motor spin more quickly

Answer 1

• Increase the strength of the magnets and thus the magnetic field
• Increase the number of turns of wire in the coil
• Increase the current to the coil from the power supply

Question 2

coil (armature) in dc motor

Answer 2

Rectangular and often made up of lots of turns of current-carrying wire

Question 3

magnets in dc motor

Answer 3

Bar magnets are usually used, producing a field perpendicular to the coil, from N to S

Question 4

brushes in dc motor

Answer 4

Allow constant electrical contact with the inside of the split ring while the coil rotates – the wires would get twisted otherwise

Question 5

split ring commutator in dc motor

Answer 5

As the coil rotates, the direction of the current needs to stay the same so that the force also acts in the same direction

This is achieved using a split ring commutator

Once the coil has rotated through 180°, current continues to flow in the original clockwise direction causing the force on the left side to be up, and the force on the right side to be down

Without the split ring, the changing direction of current caused by the coil rotating through 180° would cause the coil to flip backwards and forwards

Question 6

how dc motor works

Answer 6

A turning force causes the coil to spin about the pivot. Brushes allow constant contact whilst the coil spins freely. The split ring commutator ensures that current always flows the same way around the loop. In this case, the turning force always acts in a anticlockwise direction.