Electronic Principles
Which one of the following phrases best describes residual magnetism?

Magnetism that remains in the core of an electromagnet after the current through the coil is turned off
The circular magnetic field that surrounds a conductor carrying a current
None of these
The amount of magnetic flux that is not confined to the core material of an electromagnet
The force of attraction between the poles of a permanent and temporary magnetic field

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Electronic Principles
What is the difference between a conductor and an insulator?

The difference between conductors and insulators depends on how they are used
None of these
An insulator has an excessive number of free electrons, while a conductor has a few free electrons or none at all
An insulator allows current to flow much easier than a conductor does
A conductor allows current to flow much easier than an insulator does

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Electronic Principles
The core of an electromagnet is said to be in saturation when:

the core is permitted to move freely within the coil
changing the polarity of the current in the coil changes the polarity of the magnetic field around the core
None of these
an increase in current through the coil causes no further increase in the mmf
frequent changes in the direction of current through the coil causes heating effects in the core material

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