Session 14

Capacitors

Session 5 Template

The purpose of this session it to teach you all about the various types of capacitors used as building blocks in electronic circuits. As before we shall encounter various different terminologies which will be explained in the course of our investigations.

By the end of this session the learner will be able to:

  • Desribe the construction of a given capacitors, the range of capacitance, typical voltage limits and energy stored
  • Connect a series of 3 capacitors of the same value to the virtual cat circuit and observe the results
  • Connect 3 capacitors in parallel of the same value to the virtual cat circuit and observe results
  • Complete a short report based on the given experiments

BTEC Outcomes Covered

  • Unit 6 Pass 4

Before we start lets check out how to make a capacitor

And this is for further information

 

Capacitor Construction

The basic capacitor, an electronic component that stores an electrical charge, consists of 2 parallel plates separated by a material known as a dielectric as shown below:

Basic Capacitor construction

The unit of capacitance is the Farad which for a capacitor is defined as “the amount of electric charge (measured in coulombs) required for a capacitor to change the potential difference across its plates by 1 volt”

The Farad is a very large unit. In electronics we mostly use capacitors with ratings of millionths (micro), billionths(nano) or trillionths(pico) of a Farad.

The energy stored by a capacitor is measured in Joules.

The amount of charge stored by a capacitor basically depends on 3 things. Click on each picture for further details.

Plate Area

Plate Area

Distance Between the Plates

Plate Spacing

Dielectric Material Used (Remember the dielectric is an insulator, no current flows through it)

Dielectric Material

Permittivity

Permittivity (to permit) is a measure of how well a dielectric allows (permits) the formation of an electric field (which is where the electrical energy is stored) between the two parallel plates of a capacitor. Some dielectric materials produce much stronger electric fields than other types of material.

We say they have a higher relative permittivity. Relative permittivity is measured against absolute permittivity, which is the electric field produced between 2 plates separated by a vaccuum.

Report

In order to complete your report today you are required to investigate the properties of the following types of capacitor. Check the requirements in the report template.

  • Electrolytic
  • Mica
  • Ceramic
  • Paper
  • Variable

Here is a good way to present the information for each type of capacitor.

Electrolytic Example

Practical Investigation

The following video demonstrates the difference in charge stored when capacitors are connected in parallel compared to series.

Capacitors in Series

For the final part of this session you are required to investigate the effect of replacing the LDR’s with 10 k resistors and in the first instance, connecting 3 x 0.47 uF capacitors in series between pins 1 and 2 as shown in the schematic and then testing the circuit.

Capacitors in Parallel

Describe what happens to the sound

Capacitors in Parallel

Connect 3 x 0.47 uF capacitors in parallel between pins 1 and 2 of the 555 timer and test the circuit.

Capacitors in Series

Describe what happens to the sound.

Now complete your report and you are finished for this session

 

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