Question

Steel is more suitable than soft iron to make permanent magnet because:
1. Steel has more retentivity and low coercivity than soft iron
2. Steel has low retentivity and more coercivity than soft iron
3. Steel has more retentivity and more coercivity than soft iron
4. Steel has low retentivity and low coercivity than soft iron

Answer 1

Correct Answer - Option 2 : Steel has low retentivity and more coercivity than soft iron

CONCEPT:

Permanent magnet:

• Substances that at room temperature retain their ferromagnetic property for a long period of time are called permanent magnets.
• Permanent magnets can be made in the following ways:
  1. By holding an iron rod in the north-south direction and hammer it repeatedly.
  2. By holding a steel rod and stroke it with one end of a bar magnet a large number of times.
  3. An efficient way to make a permanent magnet is to place a ferromagnetic rod in a solenoid and pass a current.
• The hysteresis curve allows us to select suitable materials for permanent magnets.
• The hysteresis curve should be tall and wide for the material that is used to make a permanent magnet.
• The material that is used to make a permanent magnet should have high retentivity and high coercivity.
• Steel is a one-favored choice to make a permanent magnet.
• Other suitable materials for permanent magnets are alnico and cobalt steel.

EXPLANATION:

• The material that is used to make a permanent magnet should have high retentivity and high coercivity.
• Steel has a slightly smaller retentivity than soft iron but this is outweighed by the much smaller coercivity of soft iron. Hence, option 2 is correct.