Which description best defines a solenoid?

Which description best defines a solenoid?

• A. A solid bar magnet
• B. A coil of wire forming circular loops stacked along its length
• C. A capacitor with plates
• D. A single loop of wire

Answer: (B)

The idea being tested is how a solenoid creates a magnetic field by using many turns of wire arranged along a length. When current flows through a long coil of circular wire turns stacked together, each loop contributes a magnetic field, and the fields add up to produce a strong, fairly uniform magnetic field inside the coil, with a distinct north and south end. That behavior—many circular loops of wire lined up along the length to form a magnetizable tube of field—is exactly what the description describes: a coil of wire forming circular loops stacked along its length. A solid bar magnet is a permanent magnet with a fixed field, not produced by current through a coil. A capacitor with plates stores electrical charge, not a magnetic field produced by a wound coil. A single loop of wire can produce a magnetic field, but it doesn’t create the long, uniform field along a length that characterizes a solenoid.

The idea being tested is how a solenoid creates a magnetic field by using many turns of wire arranged along a length. When current flows through a long coil of circular wire turns stacked together, each loop contributes a magnetic field, and the fields add up to produce a strong, fairly uniform magnetic field inside the coil, with a distinct north and south end. That behavior—many circular loops of wire lined up along the length to form a magnetizable tube of field—is exactly what the description describes: a coil of wire forming circular loops stacked along its length.

A solid bar magnet is a permanent magnet with a fixed field, not produced by current through a coil. A capacitor with plates stores electrical charge, not a magnetic field produced by a wound coil. A single loop of wire can produce a magnetic field, but it doesn’t create the long, uniform field along a length that characterizes a solenoid.