Final answer:
A relay is an electromagnetic device that switches with current flow through its coil in electromagnets. Solenoids and toroids are widely used in different instruments for their magnetic field properties.
Explanation:
A relay is an electromagnetic device that can operate a switch when current flows through its coil. It is commonly used in applications where a low-power signal controls a high-power circuit.
In electromagnets, a coil of insulated wire wrapped around an iron core generates a magnetic field whose strength is proportional to the current flowing through it.
Solenoids and toroids are common electromagnetic devices used in various instruments, with solenoids being long wires wound in the form of a helical coil.
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