Capacitance formulas [Capacitance, Voltage, Charge Calculations]

The capacitor is an electrical device which is used to store the charge. Its basic construction involves two parallel plates which are separated by a dielectric material. During its working, some charge is transferred to its plates as a result of which a potential difference V is created between the plates. The charge transferred to the plates of capacitors depends on the capacitance and potential difference across it. The basic equation on capacitors which relates capacitance, voltage, and charge is:

Q = CV

Where in above formula:
Q = Charge in coulombs
C = Capacitance in Farad
V = Voltage in volts

We can utilize the above equation to calculate three different parameters.

Capacitor formulas
To calculate the charge Q = CV
To calculate voltage V =
Q / C
To calculate capacitance C =
Q / V

How to calculate charge

The charge is the physical property of a material and it is directly proportional to capacitance times voltage supplied to the plates.

Example # 1: The capacitance of a parallel plate capacitor is 10 pF. Find the quantity of charge on plates when the potential difference is 20 volts.

Solution: Let’s convert the pF to F for simplification of calculations:

C = 10 pF = 10 * 10-12 F

Now charge Q = 10 * 10-12 F * 20 V = 2 * 10-10  C or 200 pC

How to calculate voltage

The voltage on the capacitor is defined as the ratio between charge to the capacitance.

Example # 2: A parallel plate capacitor has a capacitance of 5 pF. Find the volts which cause the storage of 20 nC on the plates.

Solution: V = Q/C = 20 µC/5 pF = 4 kV

How to calculate capacitance

Generally, the capacitance of the capacitor is defined as the ratio between charge and potential difference. By definition, the capacitance is defined as the ratio between charge and potential difference.

Example # 3: A ceramic cap stores 20 µC when a potential difference of 30 V is applied across its ends. Find the capacitance.

Solution: C = Q/V = 20 µC/30 V = 0.66 µF

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