Capacitor
You noted that capacitors are devices that store electromagnetic energy in an electric field. Would you explain?Consider the arrangement below:
For a constant current there must be continuous charge flow. When the switch is connected, the plates are connected to a voltage source (battery), and initially the electrons start to flow from the negative electrode. However, there is a gap, which interrupts the flow. Usually, the electrons cannot just spur into the gap because the forces that keep them in the wire are far greater, thus the negative charges start to accumulate at one end of the plate. Due to this accumulation, the electrons in the plate at the other side of the gap experience repulsion and start to flow towards the positive electrode of the battery. Thus, we can say that positive charge accumulates at the top plate. Recall that there exist electric field between a region if there is a negatively charged plate and positively charged plate separated by some distance or the region.
How long will this accumulation go on?
Note that the electrons initially start to flow due to the voltage provided by the battery. Recall that voltage is a measure of the tendency of attraction between the positive charged plate and the negative charged plate. In other words, voltage is a measure of the strength of the electric field.
When the voltage between the capacitor plates equal that of the battery, there exist no voltage difference, thus electrons will stop flowing or stop accumulating at the plates. The exact details of the timing and values involved can be preciously analyzed, and will be done later.
Let me provide a scenario. Assume there exist a simple circuit where the charges are flowing. If a conducting wire is brought near to, there will be an electric field because the negative charges flowing in the circuit would repel the negative charges in the wire and positive charges will appear as shown in the Figure.
Theoretically, you are right. There will be an electric field between a conducting wire and any conducting medium near it. Practically, not all electric fields are significant in affecting the circuit behavior.
What happens to the electric field or voltage established in the capacitor?
Establishing voltage or electric field in the capacitor is called charging. The energy stored in the electric field can be used or de-charged if a circuit is connected as in the following case.
Initially, when the switch is turned on in first Figure, the charges flow, with the exception at the gap, and there is a current flow. How is the initial current and applied voltage related?
The circuit determines the current that will flow in a capacitor. If a greater voltage is applied, the accumulation of charges at the plates will be faster and the apparent current flow high.
Note that there exists a direct proportional relationship (for general use capacitors) between the charges accumulating at the plates (Q) and the voltage across the plate (V). Recall, that voltage is the measure of the strength of the electric field.
The linear constant that equates the relationship is called the capacitance. Thus, the relationship between the charges accumulating at the plates and the voltage induced across the plates is Q=CV.
Recall that the current is i=dq/dt. Thus, the current flowing in the capacitor (note that charges don't actually flow between gap under operational conditions) and the voltage across the capacitor (not the voltage applied) are related as follows dq= i dt and i = C dv/dt.
What is capacitance?
Capacitance is the linear constant that equates Q and V. It is indicative of how fast the accumulating of charges in the plates of the capacitor increase the voltage across the capacitor.
The capacitance is measured in Farads. The typical values of capacitor are small, in the range of micro, nano or pico.
Capacitor is able to store electromagnetic energy in the form electric field. In that sense it is a storage device, and a source for electromagnetic energy. How is a capacitor different from a battery?
Capacitor is not a source of electromagnetic energy in the same sense that a battery is a source of electromagnetic energy. Capacitor is a storage device because it stores the energy from another source in the electric field. On the other hand, battery is a source of electromagnetic energy-a chemical source.
Batteries provide a steady charge flow. On the other hand, a capacitor can store and discharge charges quickly. This capacity is useful in many applications.
What are the applications of the capacitor?
How is does a capacitor look like physically?
The two main types of capacitors that I used are electrolytic (Figure 1) and ceremic (Figure 2) capacitors.
(Figure 1 Source: http://www.angela.com/catalog/capacitors/Elna_Cerafine.html)
(Figure 2 Source: ?)
What is the difference between electrolytic and ceremic capacitors?
I do not know the theoretical details. Practically, when mounting the electrolytic capacitors the polarity (+ve -ve sides) matters, and for ceremic capacitors the polarity does not matter. Also, the values are inscribed in the capacitors using different conventions.
Usually, for electrolytic capacitors the value of the capacitance and the maximum operational voltage are directly inscribed.
For ceremic capacitors, you will have to calculate the capacitance values from the numbers noted in the capacitors, and you will have to refer to data sheets for the maximum operational voltage. You can calculate the capacitance values as follows:
103 = 10x103 pF= 10 nF = 0.01 microF
Note that the first two digits are multiplied the number third digit raised to 10. By convention, the result has a value in picoFarads. Another example is as follows:
222=22x102 pF= 2.20 nF
What is the maximum operational voltage?
The maximum operational voltage is an indication where capacitors will break down. The capacitor will operate normally under the maximum operational voltage value.
Are capacitors produced in all values
No. You can combine capacitors in parallel and series in such a manner that you can effectively have any value.
What is the resultant capacitance value when you place capacitors in series?
The capacitors in series are similar to resistors in parallel.
The resultant value can be found as: 1/Ct = 1/C1 + 1/C2 + 1/C3
What is the resultant capacitance value when you place capacitors in parallel?
The capacitors in parallel are similar to resistors in series.
The resultant value can be found as: Ct = C1 + C2 + C3
Where can I find more information about capacitors?