Half Wave Rectification
If a source of alternating voltage is connected in sereis with a diode or a diode - resistor combination for a suitable resistance, the output will consist of of a series of current pulse, with the crrent flowing in only one direction through the diode.
Supply and output voltages can be shown together on a double beam oscilloscope, cleary showing that the current has been truncated in one direction. Notice that the peak output voltage is less than the peak input voltage as some voltage is used to drive current through the diode.
It is not necessary to use a resistor. Half wave rectification may also be achieved with a diode - capacitor combination, or a capacitor - resistor - diode combination. If a capacitor in the circuit,a smoother output voltage is obtained since the capacitor acts to store charge.