Magnetic force on a current-carrying wire

Inside a current-carrying wire, charged particles (electrons!) are moving. When one such wire is near another, each wire creates a magnetic field that exerts a magnetic force on the moving charges in the other wire. What happens? Read the text aloud
Magnetic force between two parallel current-carrying wires
The direction of the magnetic force on either wire depends on the direction current is flowing in both. If the current in the two wires is in the same direction, then applying the right-hand rule shows that the magnetic force attracts the two wires to each other, as shown in the illustration above. If the currents are in opposite directions, then the magnetic force causes the wires to repel each other. Read the text aloud
Force on a current-carrying wire in a uniform magnetic fieldThe top illustration depicts the direction of the magnetic force on each wire that is in a magnetic field, as determined by using the right-hand rule. But what is the magnitude of the force? Intuitively, we should expect the magnetic force to be stronger if the length of the wire is longer, or if the current flowing through it is larger, or if the magnetic field around it is stronger—which is the relationship in equation (19.7)! Read the text aloud
(19.7) F B =ILB
FB  = magnetic force (N)
I  = current (A)
L  = length of wire (m)
B  = magnetic field (T)
Magnetic force
on a current-carrying wire
How a loudspeaker worksThe operation of the loudspeaker uses the magnetic force on a current-carrying wire (the voice coil) in a fixed magnetic field. As the signal current through the coil varies, the resulting force on the voice coil moves it up and down. The direction of current in the illustration causes the speaker cone to move upward; when the current reverses, the cone moves downward. The voice coil is attached to a speaker cone, which is often made of foam. When the cone moves up and down, it creates pressure waves—or sound!—in the air. Read the text aloud Show Moving-coil microphones
One wire is located in the plane of the page and carries current in the positive x-direction. A second wire is located slightly above it (but parallel to the plane of the page) and carries current in the positive y-direction. What is the direction of the magnetic force on each wire? Show

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