Power supply experiment. Power pack (left) and oscilloscope (right) being used in an experiment to demonstrate rectification. The oscilloscope is being used to examine the direct current (DC) from the power pack. The waveform on the oscilloscope screen is rectified alternating current (AC). The negative bit of the mains AC power supply has been converted to positive current (which is why half the screen is blank). DC supply from a battery would produce a straight line on the oscilloscope. This varying DC supply can be smoothed to a normal DC supply using a capacitor. A non-rectified AC and smooth DC supply are shown in image T194/646.