Capacitors

Chapter III

Capacitors

Every day, there are changes in our lives. There is a need to adapt the changes that we may encounter. There is a need to consider our nature and the readiness to counteract those changes. One of the ways in order to be ready is to store a bank of knowledge in our mind. We may use them as a key in order to survive. One of the observable changes is the modernization of our living particularly on the usage of modernized gadgets. We are living in the world where appliances or any electronic devices are widely used. We enjoy using them for recreational and for a lot of purposes. As we all know, they are used until such time that they would be damaged and they can’t be used anymore. The manufacturing companies of those appliances put a certain element to reduce the damages of fluctuating current at home or offices. This circuit element will be discussed thoroughly in this chapter. These are called capacitors.

 

http://goo.gl/gqcmNx

Capacitors are devices that are used in order to store energy. They are used in different electrical equipment like radios and televisions and others. They have the symbol of:
 
http://goo.gl/1pIyfr

They consist of one or more pairs of conductor separated by an insulator. They store electric charges. The good insulating material could be waxed paper, mica ceramic or some form of liquid gel used in electrolytic capacitors. Instead of those materials, air could also be used as separator of the plates. The insulating layer between capacitors is called dielectric. This can be shown in the figure.

 
http://goo.gl/9e5TXV

       There are two processes involved in the capacitors. These are charging and discharging. Charging means adding electrical energy while discharging means releasing the energy. We can charge by simply connecting them up to the circuit and the charges are built on the plates. We can also discharge by simply turning off the power.

Capacitance of Capacitors

The amount of electrical energy a capacitor can store is called its capacitance. The capacitance of a capacitor is like a basin. If the basin is bigger, the more amount of water can be stored.  If the capacitance is greater, then the amount of energy that can be stored is also greater. There are three ways in order to increase the capacitance. They are increasing the size of the plates, moving the plates closer together, making use of good insulator as dielectric.   

How to measure capacitance?

The unit for capacitance is farad. It is equivalent to a charge of one coulomb is stored on the plates by one volt. Capacitance, C is always positive and has no negative units. It is measured through the unit, farad, named for English electrical pioneer Michael Faraday. The formula for capacitance is                                                                                                       

Where Q is the charge

      C is the capacitance and

V is the voltage.

Types of Capacitors

There are many different types of capacitor that can be used. We can discuss them one by one.

·         Ceramic capacitor:  The capacitance values ranges from a few picofarads to around 0.1 microfarads. They are inexpensive capacitor.

·         Electrolytic capacitor: This is polarized capacitor. The capacitance value is above 1μF.

• Tantalum capacitor:   This is also polarized. It has a high capacitance level
• Silver Mica Capacitor: This has high levels of stability. This has a limited capacitance value to 1000 pF.
• Polystyrene Film Capacitor: This is inexpensive capacitor but could give a close tolerance
• Polyester Film Capacitor:  This has a consideration of cost but do not offer great tolerance.

·         Metallised Polyester Film Capacitor: This is a form of polyester film capacitor. The difference is the polyester films are metalized.

·         Polycarbonate capacitor: This has been used for reliability and performance are great. 

• Polypropylene Capacitor:   This uses a polypropylene film as the dielectric.
• Glass capacitors: These capacitors use glass as the dielectric. 
•  Supercap: From the name itself, this has great value of capacitance which could reach up to thousands of farad.

Capacitors in Parallel

If capacitors are connected in parallel manner, the formula would be:

Capacitors in Series

If the capacitors are connected in series, the formula would be:

                                                           

Experimental Data:

V_OUT: 4.5 V , R₁ = 5500 Ω , R₂ = 180 Ω, C= 4700uF

t (s)	VDROP , Charging	VDROP, Discharging	Current, Charging
5	0.4 V	2.0 V	6.6 x 10-4 A
10	0.6 V	1.8 V	5.4 x 10-4 A
15	1.0 V	1.6 V	4.50 x 10-4 A
20	1.2 V	1.4 V	3.74 x 10-4 A
25	1.4 V	1.2 V	3.10 x 10-4 A
30	1.6 V	1.1 V	2.60 x 10-4 A
35	1.8 V	1.0 V	2.13 x 10-4 A
40	2.0 V	1.0 V	1.77 x 10-4 A
45	2.05 V	0.9 V	1.46 x 10-4 A
50	2.2 V	0.8 V	1.21 x 10-4 A
55	2.2 V	0.8 V	1.01 x 10-4 A
60	2.2 V	0.6 V	8.35x 10-5 A

Graphical Representation:

References:

http://www.explainthatstuff.com/capacitors.html

http://www.radio-electronics.com/info/data/capacitor/capacitor_types.php

http://images.tutorvista.com/cms/images/83/capacitor.jpg

 http://i.stack.imgur.com/as0hm.gif)

            http://ecee.colorado.edu/~mathys/ecen1400/labs/CapacitorsInKit.jpg