Chapter 21: Electromagnetism

 1.    In an electromagnet, adjusting the variable resistor alters the size of the current. Explain the effect on the strength of the electromagnet.

• Increasing the resistance of the variable resistance will decrease the current flowing through the wire which will decrease the size of the magnetic strength of the electromagnet.

       What other methods are there to increase the strength of the electromagnet.

• Increasing the number of turns in the coil.

• Inserting a soft iron core.

 2.    *State the function of the split-ring commutator in a d.c. motor.

• The purpose of the split-ring commutator is to reverse the direction of the current in the coil every half a revolution to ensure that the coil will always rotate in one direction.