Electromagnetsim-d.c Motors

Question 1

What can increase the turning effect of a current carrying wire coil?

Answer 1

1) increase number of turns in wire coil.

2) increase current in wire coil

Question 2

1)What is the structure of a d.c. motor

Answer 2

A rectangular wire coil ABCD is mounted on an axle that allows it to rotate about PQ.
The coil and the axle are positioned in between the poles of a permanent magnet
Ends of coil ABCD are connected to a split-ring commutator. The commutator rotates with the coil
2 carbon brushes press lightly against the commutator.

Using Fleming’s left hand rule, a downward force acts on AB while upward force acts on CD. Thus coil rotates anti clockwise about axle until it reaches vertical position

Question 3

2) what is the structure of a dc motor

Answer 3

When coil is in vertical position, current is cut off as split ring commutator is not in contact with carbon brushes.
However, momentum of the coil carries it past vertical position.

Question 4

3) what is the structure of dc motor

Answer 4

The direction of currents flowing is now reversed. An upward force acts on AB and downward force acts on CD.
Hence coil rotates in anticlockwise direction.

Question 5

What is the function of the split ring commutator

Answer 5

It is to reverse direction of current every half a revolution. This occurs whenever commutator changes contact from one brush to the other.>ensures that coil will always turn in 1 direction.

Question 6

How can the turning effect of a current carrying coil in a dc motor be increased

Answer 6

Inserting soft iron core into the coil
Increase number of turns in the coil
Increase current in coil