State two ways through which the strength of an electromagnet can be increased.

Figure shows a coil wound around a soft iron bar XY. (a) State the polarity at the end X and Y as the switch is pressed. (b) Suggest one way of increasing the strength of the electromagnet so formed.

How is the working of an electric bell affected, if alternating current is used instead of direct current?

Name the material used for making the armature of an electric bell. Give a reason for your answer.