Which statement describes a solenoid?

Which statement describes a solenoid?

• A. A transformer is a solenoid with multiple windings
• B. A coil of wire around a uniform core forms a solenoid
• C. A solid rod magnetizes when heated
• D. A reed switch acts as a solenoid

Answer: (B)

A solenoid is a coil of wire that, when current flows through it, produces a magnetic field along its length. Putting a uniform ferromagnetic core inside the coil concentrates and strengthens that field, which is what many practical solenoids are. So describing a coil of wire around a uniform core encapsulates the essential setup that makes a solenoid function. The other statements don’t fit because they describe different devices: a transformer uses multiple windings to transfer energy between circuits, not a single coil forming a solenoid; heating a solid rod and magnetizing it isn’t about a coil-produced magnetic field; and a reed switch is a magnetic switch operated by an external field, not a coil-driven device.

A solenoid is a coil of wire that, when current flows through it, produces a magnetic field along its length. Putting a uniform ferromagnetic core inside the coil concentrates and strengthens that field, which is what many practical solenoids are. So describing a coil of wire around a uniform core encapsulates the essential setup that makes a solenoid function.

The other statements don’t fit because they describe different devices: a transformer uses multiple windings to transfer energy between circuits, not a single coil forming a solenoid; heating a solid rod and magnetizing it isn’t about a coil-produced magnetic field; and a reed switch is a magnetic switch operated by an external field, not a coil-driven device.