# Question Video: Knowing Key Terms Related to Electromagnetism Physics • 9th Grade

Which of the following is the correct description of a solenoid? [A] A solenoid is a single loop of insulated wire. Passing an electric current through it creates a magnetic field similar to that of a bar magnet. [B] A solenoid is a single straight piece of wire. Passing an electric current along it creates a magnetic field around it. [C] A solenoid is a long coil of insulated wire. Passing an electric current through it creates a magnetic field similar to that of a bar magnet.

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### Video Transcript

Which of the following is the correct description of a solenoid? A) A solenoid is a single loop of insulated wire. Passing an electric current through it creates a magnetic field similar to that of a bar magnet. B) A solenoid is a single straight piece of wire. Passing an electric current along it creates a magnetic field around it. C) A solenoid is a long coil of insulated wire. Passing an electric current through it creates a magnetic field similar to that of a bar magnet.

We see that each of these options offers a different description of what a solenoid is. The first option says it’s a single loop. The second says it’s a straight piece of wire. And the third calls it a long coil. To figure out which of these descriptions is correct, we can draw out our recollection of what a solenoid looks like.

A solenoid is a section of conducting wire that looks something like this. It consists of a series of loops made of conducting material. When it comes to factors like the diameter of the loops or even how many there are, the number of them, all that can change. And this will still be a solenoid. The essential property is that it’s a coil. It’s a series of loops in a wire.

Arranged this way, when we pass current through the wire, a magnetic field is created within the loops of this solenoid. When this happens, a magnetic field is created within and around the loops of the solenoid, a field which looks very similar to the field that would occur if a bar magnet were to replace this current-carrying wire.

Reviewing our three answer options in light of this, we see that option C corresponds to what we’ve drawn, a solenoid being a long coil, that’s what we have, of insulated wire. We saw that when we passed current through it, that creates a magnetic field like the field created by a bar magnet. A solenoid is not a single loop like option A claims. And it’s not a straight piece of wire like option B claims.

This means that option C is our choice for the correct description of a solenoid.