A device called an oscilloscope can be used to demonstrate what?

Oscilloscopes show the instantaneous voltage and shape of an electrical signal over time. It can be used to demonstrate the difference between AC and DC voltages, shapes of electrical waves forms, e.g., sine, square, triangular or other waves, frequencies, and other aspects of the signals. The instrument essentially draws a real-time graph of the voltage versus time for viewing or recording by the user.