Capacitance - juxtapix/IMA_E4I GitHub Wiki
Reading: 2.23.1 Determining Capacitance pg.97
Capacitance is the ability of a component to store electrons (charge). Large capacitance means more space to store electrons.
Every capacitor is created with a specific amount of capacitance, which is indicated on its packaging, denoting how much charge it is able to store. The unit of measurement for capacitance is the Farad, noted with the symbol F.
1 Farad is a rather large capacitance, so in practice, usually you'll see capacitor values that have multipliers:
- Picofarad (pF) = 0.000000000001 F
- Nanofarad (nF) = 0.000000001 F
- Microfarad (µF) = 0.000001 F
Charge
The amount of charge (Q) that is stored in a capacitor is defined as the voltage drop across the capacitor times the capacitance. Q = CV
Energy
When a capacitor is charged, that charge can also be thought if as energy. E = ½QV = ½CV²
- Q = charge in coulombs (C)
- C = capacitance in farads (F)
- V = voltage in volts (V)
- E = energy in joules (J)
Capacitive Reactance
"Within an ac circuit, the amount of charge moves back and forth in the circuit every cycle, so the rate of movement of charge (current) is proportional to voltage, capacitance, and frequency. When the effect of capacitance and frequency are considered together, they form a quantity similar to resistance. The unit for reactance is the ohm, just as for resistors. However, since no actual heat is being generated, the effect is termed capacitive reactance. The reactance is large at low frequencies and small at high frequencies. For steady DC which is zero frequency, Xc is infinite (total opposition), hence the rule that capacitors pass AC but block DC. For example, a 1µF capacitor has a reactance of 3.2kohm for a 50Hz signal, but when the frequency is higher at 10kHz its reactance is only 16ohm."
References: