Video: Understanding the Effect of a Uniform Magnetic Field on a Current-Carrying Wire That Is Parallel to the Field

The diagram shows a section of wire that has been positioned parallel to a uniform 0.1 T magnetic field. The wire carries a current of 2 A. What is the direction of the force acting on the wire due to the magnetic field?

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Video Transcript

The diagram shows a section of wire that has been positioned parallel to a uniform 0.1-tesla magnetic field. The wire carries a current of two amperes. What is the direction of the force acting on the wire due to the magnetic field?

Taking a look at our diagram, we see this wire, marked out in pink, with current running left to right. We see this wire is placed within a uniform magnetic field called 𝐵. And this field also points from left to right. Given the strength of the magnetic field and the magnitude of the current, we want to solve for the direction of the magnetic force acting on the wire due to the field.

What may first come to mind is the right-hand rule we used to help us figure out this force direction. Using our right hand, we might start out by pointing our fingers in the direction of the current as this rule calls for. But then when we seek to curl our fingers in the direction of the magnetic field, we notice something interesting. The magnetic field is in the same direction as the current. They point the same way.

It’s at this point we must be very careful to remember a condition of this right-hand rule. And that is that this rule will only be certain to give us the direction of the force on a current-carrying wire when the current and the magnetic field the wire is in are perpendicular to one another, at 90 degrees. And, in fact, in the special case when current and magnetic field are in the same direction or even when they’re 180 degrees opposed, in these two instances where they’re parallel or antiparallel to one another, the magnetic force on the wire is zero.

Looking back at our diagram, we find that that’s the case in this scenario. Our current and our field are moving in the same direction. They’re parallel, and therefore the force on the wire is zero. This isn’t the most common scenario, but we have seen that, in this case, it did come up. Because the current flowing in the wire and the magnetic field the wire is in are parallel, there is no force acting on the wire.

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