When a solid aluminum paddle is released see figure it immed

When a solid aluminum paddle is released (see figure), it immediately comes to a halt in the gap between the north and south poles of two cylindrical magnets, instead of swinging freely. This occurs even though the magnetic force between the paddle and the magnets is negligibly small (i.e. Al is not ferromagnetic). A. In 3 sentences or less, explain why this occurs. [To receive credit, you must properly invoke the correct phenomenon and correct law(s) of electromagnetism in your explanation.] B. If the solid paddle were replaced by a slotted paddle (see figure below), would this increase the damping of the oscillation, decrease it, or have no effect on it?

Solution

This phenomea happens due to eddy currents.

Eddy currents are loops of electrical current induced within conductors by a changing magnetic field in the conductor, due to Faraday\'s law of induction. Eddy currents flow in closed loops within conductors, in planes perpendicular to the magnetic field. They can be induced within nearby stationary conductors by a time-varying magnetic field created by an AC electromagnet , or by relative motion between a magnet and a nearby conductor. The magnitude of the current in a given loop is proportional to the strength of the magnetic field, the area of the loop, and the rate of change of flux, and inversely proportional to the resistivity of the material.

If the paddle is replaced by a slotted paddle, the area of loop decreases and the eddy current reduces and hence the damping is less