A current flows through a wire coil of many turns. What shape is the coil's field?
A solenoid's field outside copies a bar magnet's. But a solenoid has something a bar magnet does not: an open space through its middle. What does the field do in there?
Slide a small compass through the open middle of a current-carrying solenoid, and the answer appears. Everywhere inside, the needle points parallel to the solenoid's axis. The field inside is strong, and nearly the same strength everywhere.
Back in the Fields topic, you saw how a uniform field is drawn: evenly spaced, parallel field lines. So inside the solenoid, the sketch shows straight, parallel lines, evenly spaced, parallel to the axis.
Outside, the sketch shows a bar magnet's pattern: lines leaving the north end, looping around, and returning to the south end. The two parts join. Each line runs straight through the inside, out one end, around the outside, and back in the other end.
Inside a current-carrying solenoid, how do correctly drawn field lines run?
Where is a current-carrying solenoid's field nearly uniform?
A sketch of a solenoid's field shows the inside lines bunching tightly toward one end. Is the inside drawn correctly?
Inside a solenoid, the field is nearly uniform.
A uniform field is drawn as evenly spaced, parallel lines.
Bunched lines show a field changing strength.
No. The inside lines should keep even spacing from end to end.
A sketch shows a solenoid's outside lines running straight and parallel, far from the coil. Is the outside drawn correctly?
Outside, a solenoid's field copies a bar magnet's: loops from one end to the other.
No. The outside lines should loop from the north end around to the south end.
Outside the coil, which pattern does a solenoid's sketched field follow?
Which description belongs in a correct sketch of a current-carrying solenoid's field?
A student's sketch shows the lines inside a solenoid spreading farther apart toward one end. Which correction does the sketch need?
Outside, a solenoid's sketch matches a bar magnet's. Which feature appears only in the solenoid's sketch?