Using the circuit for an electric bell,

a) Explain why the bell won't work if the elctromagnet is replaced with a permanent magnet. (2 marks)
b)Explain why the core of the electromagnet used in an electric bell must not be made from steel. (3 marks)

a) To understand why the bell won't work with a permanent magnet, we need to understand how the circuit for an electric bell functions. An electric bell circuit typically consists of a power source, a switch, an electromagnet, and a striker (a metal piece that hits the bell).

When the circuit is closed, the power source (like a battery) sends an electric current through the circuit. This current flows through the coil of wire in the electromagnet, creating a magnetic field around the coil. This magnetic field attracts the striker, pulling it towards the electromagnet. As the striker moves towards the electromagnet, it hits the bell and produces a sound.

In a permanent magnet, there is a fixed and constant magnetic field. However, this magnetic field is not generated by an electric current flowing through a coil of wire. Therefore, if a permanent magnet is used instead of an electromagnet in the electric bell circuit, there will be no change in the magnetic field when the circuit is closed. As a result, the striker will not be attracted to the permanent magnet, and the bell won't ring.

b) In an electric bell, the core of the electromagnet should not be made from steel. This is because the core material affects the strength of the electromagnet and its ability to produce a sufficient magnetic field.

When an electric current flows through the coil of wire, it generates a magnetic field. The core of the electromagnet is typically made from a material with high magnetic permeability, which means it can easily concentrate and enhance the magnetic field generated by the coil.

Steel has a relatively high magnetic permeability, so one might think it would be a suitable material for the core. However, steel also has a high magnetic hysteresis, which means it retains some residual magnetism even after the current is removed. This residual magnetism reduces the efficiency of the electromagnet and can cause it to retain some magnetism even when the circuit is open.

To avoid these issues, the core of an electromagnet used in an electric bell is usually made from a material with low magnetic hysteresis, such as soft iron or iron-nickel alloys. These materials have a lower residual magnetism and can quickly demagnetize when the circuit is open. This allows the electromagnet to turn on and off rapidly, resulting in efficient operation of the electric bell.