Читать книгу The ESD Control Program Handbook - Jeremy M. Smallwood - Страница 40

The voltage V on a conductor is related to the stored charge Q as

The variable C is the capacitance of the conductor. In electrostatics, any conductive object has capacitance; it is just the relationship between the stored charge and the object's voltage.

In practice, the capacitance of an object can vary with proximity of other conductors and materials (see Chapter 2).

A charged capacitor stores energy. The energy W stored in a capacitance C at voltage V is given by

This can also be expressed as

An object in free space (with nothing in the near vicinity) still has capacitance. For a spherical conductor of radius r in air or a vacuum, this capacitance C is

In practice, the capacitance of an object may be due in part to the proximity to several objects. If these are effectively in parallel (Figure 1.6), the effect is to add the capacitance of all component contributors C₁…C_n to get a total capacitance C_tot as

If capacitances between objects are in series (Figure 1.7), they are combined as

Figure 1.6 Capacitors in parallel.

Figure 1.7 Capacitors in series.