Question

Magnetic materials used for making permanent magnets $\left(P\right)$ and magnets in a transformer$\left(T\right)$

• A. $\left(P\right)$: Small retentivity, large coercivity
• B. $\left(P\right)$: Large retentivity, large coercivity
• C. $\left(T\right)$: Large retentivity, large coercivity
• D. $\left(T\right)$: small retentivity, small coercivity

Answer 1

The correct option is D

$\left(T\right)$: small retentivity, small coercivity

The explanation for the correct option:

Options B &D

1. Retntivity:The ability of the magnetic field remaining in the material even after removing the external source is known as Retentivity.
2. Coercivity:The amount of reverse(-ve H) external magnetizing field required to completely demagnetize the substance is known as coercivity of substance.
3. A permanent magnet (P), must be able to hold large magnetism for a long time. So they must have large coercivity and large retentivity.
4. Electromagnet and transformer cores (T) must be able to lose magnetization quickly when the current in their coils is zero. So, they must have small retentivity.
5. Permanent magnets have high retentivity which means strong magnets.
6. Permanent magnets have high coercivity which means withstanding the demagnetization.
7. The magnets in the transformer are of small coercivity and large retentivity.

Thus, $\left(P\right)$: Small retentivity, large coercivity.

Hence, option B &D is the correct answer.