Question

Under what conditions permanent electromagnet is obtained if a current carrying solenoid is used? Support your answer with the help of a labelled circuit diagram

Answer 1

Hint: Concept of permanent magnet’s characteristics and to attain those characteristics by some modification in the solenoid like DC current and steel core. AC current should not be used as it will change the polarity of ends of the magnets but the in dc current there is no change in polarity.

Complete step by step answer:
Permanent magnets are made from material having the following characteristic.
1. High retentivity- This is to be high its product a strong magnetic field
2. High permeability. Although steel has smaller retentivity than iron but is still preferred for making permanent magnets because of its much higher coercivity than iron. Steel’s magnetization is not easily destroyed by stray fields. It retains its magnetization for a long duration if once it is magnetized under a strong field.
3. High Coercivity: This is required so magnetization cannot be destroyed by temperature variations, miner mechanical damage or by stray magnetic fields.
Conditions under what a permanent magnet can be obtained from a current carrying solenoid
1. The most effective way of making a permanent magnet is to place a steel rod in a solenoid.

2. By giving DC current to solenoid
The magnetic material should be of high retentivity and should not lose it easily.
The rod gets magnetized due to the magnetic field of solenoid.
The current used is DC so that the polarities of electromagnet does not vary with time.
3. The solenoid must consist of a closely packed large number of wire coils so as to produce a strong magnetic field through its core.

Note:
A solenoid is a simple electromagnetic device having coiled electric core and when current is passed through the wire, it acts like a magnet having north and South poles at the ends of the wire on placing a magnetic material in its core, here is a great increase in magnetic effect and thus it becomes a permanent magnet.