Power Supply Filters
Power supply filters are used to smooth the waveform after rectification.
The output from a rectifier is not like DC from a battery, it's neither pure nor constant. It's actually what's known as pulsating DC.

Pages 7-6and 7-7 of your course book cover power supply filters.
A power supply filter is a low pass filter.

The simplest form of Power supply filter is simply a large value Capacitor connected across the load, This type of filter is shown below, the resistance R represents the load on the power supply.

This type of simple power supply filter is the most common form of filter in use.
More effective Power supply filters can be designed if we use a large value inductor (often called a filter choke in this application )between the rectifier and the load. The series inductor opposes changes in the circuit current the way that the capacitor opposes changes in the circuit voltage.

This type of Power supply filter is more common in High voltage power supplies as found in Valve equipment.
Several of these filters can be combined for more effective filtering, again this kind of power supply filter is most common in High voltage power supplies
The Bleeder resistor.

It's good design practice to connect a High-value resistor across the filter capacitor in a power supply. This is used to discharge the power supply when the primary voltage (Usually the mains!) is turned off. This is to prevent electric Shock in the case of high voltage power supplies and also prevent sparking or possible equipment damage when connecting equipment to the power supply. The resistor value is usually chosen so that the filter capacitor will discharge almost completely in a couple of seconds.