A solenoid acts like a bar magnet
A coil with a current has a north and a south pole.
A coil and a compass
A long coil of insulated copper wire carries a current. You look at the field lines round it and compare them with those of a bar magnet.
How do the two patterns compare?
What this lesson covers
The idea
A solenoid is a coil of many circular turns of insulated copper wire wrapped closely in a cylinder; carrying current, its field pattern resembles a bar magnet's, with one end a north pole and the other a south pole.
A coil and a compass
A long coil of insulated copper wire carries a current. You look at the field lines round it and compare them with those of a bar magnet.
How do the two patterns compare?
- They are similar
- They are completely different
- The coil has no field lines at all
Coil and magnet
Open each tab and compare the solenoid's field with the bar magnet's field.
A magnet made by current
Winding many turns of wire closely into a cylinder gives a solenoid. When it carries a current, the lines go out at one end and in at the other, like a bar magnet. So the solenoid has a north end and a south end.
A solenoid is a coil of many circular turns of insulated copper wire wrapped closely in a cylinder. Carrying current, its field pattern is similar to a bar magnet's: one end behaves as a north pole and the other as a south pole.
Notes
A current-carrying solenoid has a field like a bar magnet: one end is a north pole and the other a south pole.
Check yourself
What is a solenoid?
The magnetic field pattern of a current-carrying solenoid is similar to that of…
A solenoid carries a current. Its two ends behave like…
The field lines of a current-carrying solenoid leave it at one end, just as for a bar magnet. The end where they leave is the…
- A single circular loop of wire. A solenoid has many turns wrapped closely. A single circular loop is just one turn.
- A coil of many circular turns of insulated copper wire wrapped closely in the shape of a cylinder — correct. Yes!
- A straight wire with a current in it. A straight wire has concentric circles of field lines. A solenoid is a close coil of many turns.
- a straight wire, which has concentric circles. A straight wire has concentric circles of field lines. The field of a solenoid is similar to that of a bar magnet.
- a single circular loop, which has straight lines only at its centre. A solenoid has many turns, and its field is similar to that of a bar magnet.
- a bar magnet — correct. Yes!
- a north pole at one end and a south pole at the other — correct. Yes!
- north poles at both ends. One end of the solenoid behaves as a north pole, and the other behaves as a south pole.
- no poles at all, since it is only a coil of wire. A current-carrying solenoid behaves like a bar magnet, so it has a north pole and a south pole.
- south pole. Field lines emerge from the north pole and merge at the south pole.
- north pole — correct. Yes!
- middle of the coil. The lines leave at one end of the solenoid. As for a bar magnet, field lines emerge from the north pole.