Capacitance is one of the central concepts in electrostatics, and specially constructed devices called capacitors are essential elements of electronic circuits. But what is capacitance, and what property of objects is best measured by their capacitance?
What Is Capacitance?
Capacitance is the ability of an object to store electric charge and release it when needed. Capacitance is defined as the ratio of charge to voltage for a given object:
where C is the capacitance, Q is the charge, and V is the voltage.
Capacitance is measured in units of farads (F), which are equal to coulombs per volt (C/V). One farad is a very large unit of capacitance, so most capacitors have capacitances in the range of microfarads (µF), nanofarads (nF), or picofarads (pF).
What Property of Objects Is Best Measured by Their Capacitance?
The property of objects that is best measured by their capacitance is their ability to store charge. This property depends on the size, shape, and material of the object, as well as the distance and orientation of other objects nearby.
For example, a parallel-plate capacitor is a device that consists of two flat metal plates separated by a small distance. The capacitance of a parallel-plate capacitor is given by the formula:
where 0 is the permittivity of free space, A is the area of the plates, and d is the distance between them.
From this formula, we can see that the capacitance of a parallel-plate capacitor increases with the area of the plates and decreases with the distance between them. This means that a larger and closer pair of plates can store more charge than a smaller and farther pair of plates.
Another example is a spherical capacitor, which is a device that consists of two concentric metal spheres. The capacitance of a spherical capacitor is given by the formula:
where a and b are the radii of the inner and outer spheres, respectively.
From this formula, we can see that the capacitance of a spherical capacitor increases with the radii of the spheres and decreases with the difference between them. This means that a larger and closer pair of spheres can store more charge than a smaller and farther pair of spheres.
Why Is Capacitance Important?
Capacitance is important because it determines how much charge and energy a capacitor can store and how fast it can release it. Capacitors are widely used in electronic circuits for various purposes, such as:
- Filtering: Capacitors can smooth out the fluctuations in the voltage or current of a circuit, such as removing noise or ripple from a power supply.
- Timing: Capacitors can create delays or oscillations in a circuit, such as generating pulses or waves of a certain frequency or duration.
- Coupling: Capacitors can transfer signals or power from one part of a circuit to another, such as isolating the direct current (DC) component or amplifying the alternating current (AC) component.
- Storing: Capacitors can store charge and energy for later use, such as providing backup power or boosting the voltage.
How to Measure Capacitance?
There are several methods to measure capacitance, depending on the type and value of the capacitor and the accuracy and precision required. Some of the common methods are:
Using a multimeter:
A multimeter is a device that can measure various electrical quantities, such as voltage, current, resistance, and capacitance.
To measure capacitance with a multimeter, the capacitor must be disconnected from the circuit and discharged, and then connected to the multimeter probes. The multimeter will display the capacitance value in farads or subunits of farads.
Using a frequency meter:
A frequency meter is a device that can measure the frequency of an AC signal, such as a sine wave or a square wave. To measure capacitance with a frequency meter, the capacitor must be connected to a circuit that generates an AC signal of a known frequency and amplitude, such as an oscillator or a function generator.
The frequency meter will measure the frequency of the signal across the capacitor, which is inversely proportional to the capacitance value.
Using a bridge circuit:
A bridge circuit is a circuit that consists of four resistors or capacitors arranged in a diamond shape, with a voltage source and a detector connected across the opposite corners.
To measure capacitance with a bridge circuit, the capacitor must be connected to one of the arms of the bridge, and the other arms must be adjusted until the detector shows zero or minimum voltage. The capacitance value can be calculated from the values of the other arms of the bridge.
Capacitance is the ability of an object to store electric charge and release it when needed. The property of objects that is best measured by their capacitance is their ability to store charge, which depends on the size, shape, and material of the object, as well as the distance and orientation of other objects nearby.
Capacitance is important because it determines how much charge and energy a capacitor can store and how fast it can release it.
Capacitors are widely used in electronic circuits for various purposes, such as filtering, timing, coupling, and storing. Capacitance can be measured by various methods, such as using a multimeter, a frequency meter, or a bridge circuit.