# Question Video: Understanding the Effect of a Uniform Magnetic Field on a Current-Carrying Wire That Is Parallel to the Field Physics • 9th Grade

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?

Okay, in this diagram, we see this section of wire here, which is parallel to a uniform magnetic field. The diagram also shows us that charge in the wire moves left to right. Based on this, we want to solve for the direction of the force that acts on this wire due to the magnetic field. Now, we have to be a bit careful here. Seeing that we have a current-carrying wire in a magnetic field, we might think of the mathematical relation for the force on such a wire.

That equation says that this force is equal to the strength of the magnetic field multiplied by the current magnitude in the wire times the length of the wire exposed to the field. But there’s an important condition that’s required in order for this equation to be valid. The condition is that the magnetic field direction is perpendicular to the direction of current in the wire. In our case though, we can see that condition is not met because the current and the magnetic field point parallel to one another. When this is the case, this equation here for magnetic force doesn’t apply. And, in fact, the magnetic force experienced by this current-carrying segment of wire is zero when the current and magnetic field are parallel. In other words, the force acting on this section of wire is zero.

Now, we’re not asked about the force magnitude itself, but rather its direction. We can see though that this realization impacts our answer to the force direction. That’s because a force of zero has no direction to it. So our answer to this question can simply be that there is no force acting on the wire. Since there’s no force, there’s no direction. And this then is our answer.