Retentivity and coercivity of permanent magnets and magnets used in transformers

In the context of permanent magnets and materials used in transformers, "retentivity" and "coercivity" are properties related to the magnetic behavior of materials.

1. Retentivity (Remanence): Retentivity, also known as remanence, is the ability of a magnetic material to retain a certain level of magnetization after an external magnetic field is removed. In other words, it measures how well the material "remembers" its magnetization. A material with high retentivity will retain a strong magnetic field even after the external magnet is taken away. Permanent magnets, like the one denoted as P in your question, typically have high retentivity, as they are designed to maintain a strong magnetic field without an external source.

2. Coercivity: Coercivity, on the other hand, is the measure of the resistance of a magnetic material to becoming demagnetized when an external magnetic field is applied in the opposite direction. It quantifies the amount of reverse magnetic field strength required to reduce the material's magnetization to zero. Materials used in transformers, like the one denoted as T in your question, usually have low coercivity because they need to respond to changes in the external magnetic field quickly and efficiently. Low coercivity ensures that they can be easily magnetized and demagnetized as needed in transformer operation.

So, in summary:

• Permanent magnets (like P) have high retentivity and High coercivity because they are designed to maintain a strong magnetic field.
• Materials used in transformers (like T) typically have low coercivity and low retentivity to respond effectively to changes in the external magnetic field.