There are many different practical capacitors available. It depends on the dielectric present between the two positive and negative plate of the capacitor. A capacitor dissipates a negligible amount of electrical energy.
A capacitance of a capacitor is the ability to store electrical energy, some capacitors have a higher capacitance than others, Farad is the SI unit of a capacitance of a capacitor, the capacitance of a capacitor ranges from picofarad to millifarad. One farad = 1coulumb/voltage.
Capacitors are widely used in electronic circuits. Ceiling fans have a capacitor, capacitors in electronic circuits are used to block DC current, it is also used as a filter, like a tuning device. A resistor combined with a capacitor in series makes a timing circuit.
Capacitor symbols Fixed and variable
Theory of a capacitor
When two conductors are separated by an insulator, be it air or some kind of an insulator, a capacitor is formed.
Practical capacitors are made up of two plates separated by a dielectric. A dielectric is an insulator.
When a voltage is applied across a capacitor the dielectric becomes polarized and develops the electric field, the conductive plates hold equal and opposite charges on their facing surfaces.
The charge stored by a capacitor is directly proportional to the applied voltage. the C is the proportionality constant, which is the capacitance of the capacitor
This means as the area of the plates is increased the capacitance also increases. Furthermore, if the dielectric material placed has a higher permittivity, the capacitance increases also.
The energy stored by a capacitor
Capacitors store electrical energy in the form of an electric field. When a voltage is applied across a capacitor, the capacitor stores the electrical energy, the voltage across the plates of the capacitor starts to rise until their voltage reached the applied voltage. A given capacitor with 22uF 400V connected to 400V power supply, the voltage of the capacitor will keep rising until it reached 400V. the capacitor is charged to 400V!!. So care must be taken when handling a circuit with capacitors that are connected on a power source, even when the power is cut.
Charge and discharge of a capacitor
When a capacitor is connected across a DC source, one of the plates becomes positively charged and the other becomes negatively charged.
Capacitors block DC.
When a capacitor is connected across an alternating current, one of the plates become positively charge and the other becomes negatively charged, the capacitor continuously charges and discharge, Alternating current flows. However, this current is not a conventional current it is called displacement current due to the displacement charge. Currently doesn't actually flow through a capacitor.
The displacement current is given as.
and the displacement voltage is.
Charging a capacitor through a resistor
When a capacitor is connected in series with a resistor, and voltage is applied across them. The rate at which the capacitor charges depends on
i) The capacitance of the capacitor
ii) The value of the resistor in series with the capacitor
When a capacitor is charging through a resistor to a final voltage. The instantaneous voltage is given as
Discharging a capacitor through a resistor
When a charged capacitor is connected to a resistor, the capacitor discharges through the resistor. The rate at which the capacitor discharges depends on the value of the capacitor and the resistor. The instantaneous voltage of the capacitor is
Capacitors in parallel
When two or more capacitors are connected side by side as in the figure below they are said to be in parallel, the potential difference across both the capacitors is the same.
Capacitors in series
When two or more capacitors are connected end to end they are said to be in series. The voltage across the capacitors is not the same. And the resultant capacitance is
And the sum of the capacitance in series is.
RC filter
The RC filter is a frequency-dependent voltage divider. They are used to block either a high-frequency signal or low-frequency signal depending on the RC arrangement.
High pass filter
This is a capacitor-resistor voltage divider circuit. This circuit blocks low-frequency signal (DC) from passing while allowing high frequency signal AC.
Low pass filter
This is a resistor-capacitor voltage divider circuit. This circuit blocks High-frequency signal (AC) while allowing a low-frequency signal to pass.
Types of a capacitor
There are generally two types of capacitors Polarized and non-polarized.
A polarized capacitor has to be connected correctly in a circuit with a positive leg connected to the higher potential in the circuit and the negative leg to the lower potential in the circuit.
Electrolytic capacitor
Generally, they are polarized capacitors, they contain an electrolyte as a dialectic. They fall into a category, 1 Aluminum capacitor, Tantalum Capacitor, Niobium Capacitor.
Ceramic capacitor
Ceramic capacitors have a ceramic as a dielectric. Usually, it is a mixture of ceramic and titanium dioxide. Some ceramic capacitor is mixed with barium titanate.
Mica capacitor
These type of capacitors are reliable and they have a high precision they are also called silver mica capacitors, they have mica as a dielectric material, they are used in a high-frequency application. Their apacitance ranges between 1pF-0.1μ
Air Capacitor
These have air as a dielectric, they are used as variable capacitors
Paper capacitor
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