Steps in manufacturing the oscillating dee:
The real fun is when you see the induced emf grow as you keep on winding multiple turns of wire around the solenoid. You start unwinding or winding a few turns in the opposite sense, the induced emf starts to drop. When the same loop’s position is changed so that it does not enclose the primary solenoid, the induced emf drops again to zero. If the bunch of wires are placed vertically inside the primary, no emf is developed. Furthermore, change the frequency and notice the dependence of the induced emf. Last, the phase difference between the source and induced voltages is a clear demonstration of the time derivative of a sinusoid.
However, the metallic plate with slots experiences very less effects of the magnetic field and takes longer to come to a stop. This is because due to inconsistent surface it will not have circular electric currents and thus will not have the right magnetic field to oppose its movement against the field of electromagnet.