An electromagnet is a device in which moving electric charges (current) in a coil of wire create a magnet. what’s one advantage of using electromagnets in devices?
a. electromagnets have a strong, constant magnetic field.
b. electromagnets are more powerful than permanent magnets.
c. electromagnets don’t need a source of electricity to work.
d. electromagnets can easily be turned on and off.

D.Electromagnets can easily be turned on and off.

Explanation:

An electromagnet is a device which moving electric charges(current) in a coil of wire create a magnet. Electromagnets can easily be turned off and on because it is a electromagnet. When current flows through a wire, a magnetic field is produced around a wire and create an electromagnet. The coils are always made of copper wire because copper is a good conductor of electricity.

Advantage of using electromagnetic devices:

Electromagnet over a permanent magnet: It is the magnetic field can be sudden changed by the controlling the amount of electric current in winding. It needs no power, an electromagnet needs continuous supply of current to maintain the magnetic field.

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he forelimbs below belong to four species that descended in a direct line from the ancestral mammal shown above. of the four descendants shown, which species most likely appeared earliest in evolutionary history?