A capacitor is like a battery because it stores electrical energy. The difference between a capacitor and a battery is, it does not produce new electrons but only stores them.
Covered in this Article
In this article, you will learn:
- What a capacitor is
- Symbols of a capacitor
- What Capacitance of a capacitor means
- How a capacitor is made
- How a capacitor works
- How to test a capacitor
- Applications of a capacitor
What Is a Capacitor?
A capacitor is a two-terminal electrical/electronic device that stores energy temporally It is commonly referred as “caps” and it is one of the fundamental passive components just like resistors and inductors. it is also one of the most commonest used components just like resistors. There are many different types of capacitors available in the market, but they all do the same thing, they store charge.
Symbols of a Capacitor
These are the common ways used to represent a capacitor in an electronic schematic.
Each capacitor should be represented by the letter – C1, C2, etc and a value. The value should show the capacitance of the capacitor; that is, how many farads it has.
The Capacitance of a Capacitor
Capacitance is defined as being that a capacitor has the capacitance of One Farad when a charge of One Coulomb is stored on the plates by a voltage of One volt.
It can be mathematically expressed as C=Q/V which can be rearranged as Q=CV
One farad is defined as the capacitance which stores a one-coulomb charge across a potential difference of one volt between its plates.
The capacitance of a capacitor is the ability of a capacitor to r is the ability of a capacitor to store electrical charge. It is measured in farad ( unit of capacitor), which is abbreviated with the letter ‘F’ named after the British physicist Michael Faraday.
The prefix of farad ranges from picofarad to Megafarad.
|Prefix Name||Abbreviation||Equivalent Farads|
|Picofarad||pF||0.000000000001 or 10-12 F|
|Nanofarad||nF||0.000000001or 10-9 F|
|Microfarad||µF||0.000001 or 10-6 F|
|Milifarad||mF||0.001 or 10-3 F|
|Kilofarad||kF||1000 or 103 F|
|Megefarad||Mf||1000000 or 106|
Kilofarad and Megafarad are special caps known as super or ultra-capacitors.
How a Capacitor Is Made
A capacitor is made from two metal plates and an insulating material called a dielectric. The metal plates are placed parallel to each other, in a very close range. An insulating material (dielectric) is placed between these two plates to prevent them from touching each other.
The insulating material can be paper, mica, glass, ceramic, air, rubber, wood, ceramic, plastic, or anything that will obstruct the flow of current.
The plates are made of conductive materials like silver, aluminum disks, aluminum foil, or a thin film of metal. Factors affecting the capacitance of a capacitor (how many farads) are:
- Plate Area (A): The greater the plate area, the greater the capacitance and vice versa.
- Distance (d): The greater the distance of the two conductive plate, the lesser the capacitance and vice versa.
- Dielectric material (Ɛ): The greater the permittivity of the material, the greater the capacitance and vice versa
. The total capacitance of a capacitor can be calculated with the equation:
Where C is capacitance in farads
Ɛr,is the dielectric’s relative permittivity (a constant value determined by the dielectric material)
A is the area the plates overlap each other in square meters
d is the distance between the plates in meters
How a Capacitor Works
A capacitor comprises two parallel plates. When these plates are connected to a voltage (dc) source like battery, electrons are “pushed” towards one plate by the negative terminal of the battery, while electrons are “pulled” from the other plate by the positive terminal of the battery. If the charge differences between the two metal plates become very large, a spark may fall across the gap between them and discharge the capacitor. A dielectric material is placed between them to act as spark blocker and helps to increase the charge capacity of the capacitor.
How to test a Capacitor
A capacitor can be tested by using a multimeter ( click in order to know how to test a capacitor) or using the traditional method, that is short circuiting the capacitor.
You must be careful when using the traditional method to test a capacitor. If you want to test a capacitor, for example a fan’s capacitor,etc.
Follow these steps:
- Disconnect the capacitor from the fan.
- Now connect the leads (wires) of the capacitor to 230 V AC Supply for a very short time (about 1-5 Seconds)
- Remove leads from the 230 V AC Supply.
- Now place the two leads of the capacitor together (Please Be Careful to do that).
- If it gives a strong spark, it means the capacitor is good.
- If it doesn’t make a spark or it makes a weak spark, it means the capacitor is bad.
Applications and uses of Capacitors
- Timing – Capacitors are used along with resistors in time-dependent circuits like an oscillating blinking light.
- Smoothing -It is used in the conversion of AC to DC by smoothing the current of alternating current supply.
- Tuning – A Variable capacitor is used in tuning circuits on a radio system by connecting them to an LC oscillator. It is also used along with an inductor to tune circuits to a particular frequency, an effect exploited by radio receivers, speakers, and analog equalizers.
- Sensors-A Capacitor can be used as a sensor in measuring a air humidity, fuel levels, mechanical strain, etc.
- Filters – Capacitors in conjunction with resistors are often used as the main element of frequency selective filters.
Some of the types of filter designs include:
- High Pass Filter (HPF)
- Low Pass Filter (LPF)
- Band Pass Filter (BPF)
- Band Stop Filter (BSF)
- Notch Filter
- All Pass Filter
- Equalization Filter
Warning! Capacitors can store a charge for seconds or minutes (it depends on the value of the capacitor) after the source of power to them has been switched off. This charge can be very risky. Never touch the leads of high voltage capacitors until its fully discharged