When a wire is moved downward between the two poles of a magnet, it experiences a phenomenon known as electromagnetic induction, which leads to the creation of an alternating magnetic field. This phenomenon is governed by Faraday's law of electromagnetic induction.
Faraday's law states that a changing magnetic field induces an electromotive force (EMF) or voltage in a conductor. When the wire is moved downward, the magnetic field between the two magnet poles passing through the wire changes. This changing magnetic field induces an electric current in the wire.
The direction of the induced current can be determined using Lenz's law, which states that the induced current creates a magnetic field that opposes the change in the magnetic field that induced it. In this case, the induced current creates a magnetic field that opposes the motion of the wire.
As the wire moves downward, the induced current creates a magnetic field that points upward between the magnet poles. When the wire reaches the bottommost position, the induced current and the magnetic field are at their maximum. As the wire moves further downward, the induced current decreases, and the magnetic field weakens.
The movement of the wire back upward also induces a current, but in the opposite direction. This creates an alternating current (AC) in the wire, which means that the current changes direction periodically as the wire moves up and down.
The alternating current in the wire, in turn, creates an alternating magnetic field around the wire. This magnetic field extends into the space between the magnet poles and alternates its direction as the wire moves up and down.
Thus, by moving the wire downward between the two magnet poles, an alternating magnetic field is created due to the phenomenon of electromagnetic induction. This alternating magnetic field has applications in various devices, such as generators, transformers, and electric motors.