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 if the electromagnet is replaced with a permanent magnet, we need to look at the functioning of an electric bell. In the circuit for an electric bell, a switch, a power source (battery), an electromagnet, and a metal strip called an armature are present.
When the switch is closed, current flows through the circuit. This current passes through the coil of the electromagnet, creating a magnetic field around it. The armature, which is attracted to this magnetic field, moves towards the electromagnet, causing the bell to strike against a gong, producing sound.
If we replace the electromagnet with a permanent magnet, the magnetic field produced by the permanent magnet remains constant, regardless of the current in the circuit. As a result, there would be no variation in the magnetic field strength to attract and repel the armature. Without this variation, the armature would not move, and the bell would not ring. Therefore, the bell won't work if the electromagnet is replaced with a permanent magnet because the permanent magnet does not allow for the required attraction and repulsion needed to produce sound.
b) The core of the electromagnet used in an electric bell must not be made from steel for a few reasons. First, let's understand the purpose of the core in an electromagnet. The core provides a path for the magnetic field produced by the coil to flow through and concentrate, increasing the strength of the magnetic field.
When current flows through the coil, it generates a magnetic field. If the core is made of steel, it is highly ferromagnetic and would easily become magnetized by the magnetic field of the coil. As a result, the magnetic field lines would primarily follow the path through the core, instead of flowing through the air and attracting the armature. This means that a significant portion of the magnetic field would be trapped within the core, reducing its effectiveness in attracting the armature.
Additionally, steel is a good conductor of electricity. If the core were made from steel, it would create a closed loop circuit, allowing current to flow through it. This would create eddy currents, which would generate heat, wasting energy and diminishing the efficiency of the electromagnet.
Therefore, to prevent the core from becoming magnetized and to reduce energy loss due to eddy currents, the core of an electromagnet used in an electric bell is usually made from materials that are less ferromagnetic, such as soft iron or soft magnetic alloys. These materials allow the magnetic field to flow through and concentrate effectively while minimizing energy loss.