Why should the core of a coil of a circuit breaker be strongly magnetized when current passes through it, and immediately demagnetized when the switch is turned off?
Please try to explain the reasoning in simple words as I am only in high school.
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2 Answers
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The core probably is made of a material with high permeability, but low remanence.
"High permeability" means that the material can be strongly magnetized by an external field (i.e., by the field that the coil creates). "Low remanence" means that it does not stay strongly magnetized after the external field has been switched off.
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The magnetism comes from the electric current going through the coil. When the electrical path is open so that the current can no longer flow and maintain the magnetic field, the collapsing magnetic field will create a voltage that tries to keep the current flowing. That generates a very short lived voltage spike and at the end of it, there is no current flow to create a magnetic field.
