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