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Question Video: Understanding the Magnetic Field Created around a Current-Carrying Wire Physics • 9th Grade

Which of the four diagrams correctly shows the field lines of the magnetic field created around a current-carrying wire? The direction of the current in the wire goes through the screen.

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Video Transcript

Which of the four diagrams correctly shows the field lines of the magnetic field created around a current-carrying wire? The direction of the current in the wire goes through the screen.

In each of these four diagrams (a), (b), (c), and (d), there’s a different representation of how the magnetic field lines around a current-carrying wire appear. In each of the diagrams though, the direction of current in the wire is the same; it points into the screen.

To figure out which of these field line representations is correct, we can recall what’s called a right-hand rule for determining this field line, given current direction. If we have a wire carrying current like this, then by pointing the thumb of our right hand in the direction of that current, our fingers curl closed in the direction of the magnetic field lines around the wire. In this case then, the magnetic field around the wire would point like this.

We can now apply this right-hand rule to the current in our example that points into the screen. Pointing the thumb on our right hand in that direction, the way that our fingers are capable of curling closed is in this clockwise direction. That then is the direction of the magnetic field lines around a wire that carries current pointing into the screen. Of our four answer options, this direction is indicated in option (d). Notice that in option (d), we have concentric field lines but they all point in the same clockwise direction. Option (d) is our answer choice.

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