Physics
Physics
Problem
A square coil has its plane initially perpendicular to a uniform magnetic field that points out of the page. The coil is then rotated clockwise about a vertical axis so that the magnetic flux through the coil decreases. When viewed from the original position facing the coil, which statement best describes the direction of the induced current during this rotation? a) It is clockwise, the same direction as the rotation. b) No current is induced because the coil’s area does not change. c) It is counter-clockwise, opposing the decrease in flux. d) It alternates between clockwise and counter-clockwise each quarter-turn.Intuitive explanation
The key is Lenz's law: the induced current always opposes the change causing it. Since the magnetic flux through the coil is decreasing (the field is pointing out, but the coil is rotating away), the induced current must create its own magnetic field pointing out of the page to try to maintain the original flux. Use the right-hand rule—curl your fingers in the direction of current flow, and your thumb points in the direction of the magnetic field it creates. For the field to point outward, the current must flow counterclockwise when viewed from your original position facing the coil.
Intuitive explanation
The key is Lenz's law: the induced current always opposes the change causing it. Since the magnetic flux through the coil is decreasing (the field is pointing out, but the coil is rotating away), the induced current must create its own magnetic field pointing out of the page to try to maintain the original flux. Use the right-hand rule—curl your fingers in the direction of current flow, and your thumb points in the direction of the magnetic field it creates. For the field to point outward, the current must flow counterclockwise when viewed from your original position facing the coil.