Experimenting with slow AC
Slow AC (with frequencies less than 1 Hz) can be used to show many AC phenomena. Meters and oscilloscopes can show changing voltages and currents, and the phase differences between them.
Traditionally these phase changes can be shown with the aid of a double beam oscilloscope. However, this is quite difficult to relate to what is going on in the circuit. A slow AC device, mechanical or electronic, aids the conceptual understanding since students are able to see the slow movements of the meter pointers.