CAPACITORS
A Capacitor is a device that stores an electrical charge in an ELECTROSTATIC Field.
When two CHARGED particles, one positive the other negative, are placed in close proximity, a ELECTROSTATIC Field is developed. Because an electrostatic field is polarised positive to negative, the field is drawn from positive to negative.
If two charges are the same for example, then the charges will repel each other.
When a capacitor is placed in a circuit which is connected to a DC source, the negative plate gains an electron whilst the positive plate loses an ELECTRON. This creates a DIFFERENCE of POTENTIAL.
As the negative plate gains more electrons, it REPELS the negative voltage coming from the battery since like charges REPEL. Similarly, as the positive plate loses an ELECTRON and becomes more postive, it repels the positive voltage from the battery. A characteristic of a circuit or device to oppose the change of current or voltage in a circuit is called REACTANCE. This is a form of CAPACITIVE REACTANCE.
The EMF will tend to force the current from postive to negative, against the battery source, which is from negative to positive.
REMEMBER, as the voltage builds up across a capacitor due to the electrostatic field, the voltage drop will reduce across another device on the circuit, like a resistor or transistor. In a parallel circuit, Voltage is the same everywhere, in a series circuit, CURRENT is the same everywhere.
If you think about it for a moment, you should be able to understand why they allow AC to pass through: AC keeps reversing its polarity. As long as the AC switches fast enough to prevent the cap from becoming fully charged in any direction, then the cap will partially charge in one direction, and as the AC polarity reverses, the cap will start to discharge, then charge in the opposite direction. Very low-capacitance caps may partially block the AC because they become fully loaded before the AC cycle is complete, however.
IN AC Circuits:
When the frequency increases, the capacitor will act like a short, allowing the signal through, therefore, higher the frequency, the more of the signal is passthough, (given the capacitor size is the same)
Larger the cap, more of the signal will pass through, since the formula for Capacitive reactance is
Xf = 1 / 2pi*f*C
ONE THING THAT I FOUND
When a capacitor is connected in SERIES in a circuit that is used with AC, such as a FM bug, the capacitor is used for coupling.
When a capacitor is connected in PARALLEL, meaning the positive end is connected to the positive rail and the negative end (or the other end of the capacitor) is connected to the negative rail, then it is used to hold a charge in its electrostatic field.
The size of the capacitance of a Capacitor matters in AC Circuits. RF can use lower capacitors becuase the charging and discharging of the capacitor plates happen so quickly, that the capacitor does not block any signals - if a small farad capacitor was used in AF, then the plates would charge to the potential and block most of the Audio signal, hence we need a larger farad capacitor.
When two CHARGED particles, one positive the other negative, are placed in close proximity, a ELECTROSTATIC Field is developed. Because an electrostatic field is polarised positive to negative, the field is drawn from positive to negative.
If two charges are the same for example, then the charges will repel each other.
When a capacitor is placed in a circuit which is connected to a DC source, the negative plate gains an electron whilst the positive plate loses an ELECTRON. This creates a DIFFERENCE of POTENTIAL.
As the negative plate gains more electrons, it REPELS the negative voltage coming from the battery since like charges REPEL. Similarly, as the positive plate loses an ELECTRON and becomes more postive, it repels the positive voltage from the battery. A characteristic of a circuit or device to oppose the change of current or voltage in a circuit is called REACTANCE. This is a form of CAPACITIVE REACTANCE.
The EMF will tend to force the current from postive to negative, against the battery source, which is from negative to positive.
REMEMBER, as the voltage builds up across a capacitor due to the electrostatic field, the voltage drop will reduce across another device on the circuit, like a resistor or transistor. In a parallel circuit, Voltage is the same everywhere, in a series circuit, CURRENT is the same everywhere.
If you think about it for a moment, you should be able to understand why they allow AC to pass through: AC keeps reversing its polarity. As long as the AC switches fast enough to prevent the cap from becoming fully charged in any direction, then the cap will partially charge in one direction, and as the AC polarity reverses, the cap will start to discharge, then charge in the opposite direction. Very low-capacitance caps may partially block the AC because they become fully loaded before the AC cycle is complete, however.
IN AC Circuits:
When the frequency increases, the capacitor will act like a short, allowing the signal through, therefore, higher the frequency, the more of the signal is passthough, (given the capacitor size is the same)
Larger the cap, more of the signal will pass through, since the formula for Capacitive reactance is
Xf = 1 / 2pi*f*C
ONE THING THAT I FOUND
When a capacitor is connected in SERIES in a circuit that is used with AC, such as a FM bug, the capacitor is used for coupling.
When a capacitor is connected in PARALLEL, meaning the positive end is connected to the positive rail and the negative end (or the other end of the capacitor) is connected to the negative rail, then it is used to hold a charge in its electrostatic field.
The size of the capacitance of a Capacitor matters in AC Circuits. RF can use lower capacitors becuase the charging and discharging of the capacitor plates happen so quickly, that the capacitor does not block any signals - if a small farad capacitor was used in AF, then the plates would charge to the potential and block most of the Audio signal, hence we need a larger farad capacitor.
posted by Shelton D'Cruz at 1:41 AM
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