A metal sheet is placed in a magnetic field whose magnitude changes from zero to maximum. The direction of eddy currents produced in the plate is shown in the figure. Then the direction of magnetic field is:
Show Hint
Use the Right-Hand Grip Rule: curl your fingers in the direction of the current, and your thumb points in the direction of the induced magnetic field.
Concept:
Lenz's Law states that the direction of induced currents is such that they oppose the change in magnetic flux that produced them. If the magnetic field magnitude increases from zero to maximum, the magnetic flux through the loop increases.
Step 1: Apply Lenz's Law.
The induced eddy currents will create their own magnetic field to oppose the increasing external flux. If the flux is increasing, the induced field must point in the opposite direction.
Step 2: Determine the induced magnetic field direction.
Looking at the figure provided in the source, the eddy currents flow in a counter-clockwise direction. By the Right-Hand Rule, a counter-clockwise current loop produces a magnetic field directed outwards (perpendicular to the plane).
Step 3: Conclusion.
Since the induced field is outwards to oppose an *increasing* inward field (or simply by interpreting the current flow), the original field must be directed inwards, and the induced current generates an opposing field outwards. *Correction:* If the current is counter-clockwise, the induced field is outwards; thus the external flux causing this must be inwards. The question asks for the direction of the magnetic field causing this.
$$\boxed{\text{Normally outwards}}$$
