y by definition. Because air is nearly "empty" space, its measured dielectric constant is only slightly greater than unity. The difference is insignificant. Let L represent some geometric dimensions as a function of length. For a parallel plate capacitor with an air dielectric (insulator), L = A/d [from Eq. (A.21)]. Capacitance (C) can be related to dielectric constant, the geometrical property L, and a constant by C=EOKL (A.22) where EO is the permittivity constant, 8.85 pf/m, and K is the dielectric constant from Table A.2. Another effect of the introduction of a dielectric (insulator) including air is to limit the potential difference between the conductors to some maximum voltage value. If this value is substantially exceeded, the dielectric material will break down and form a conducting path between the plates. Every dielectric material has a characteristic dielectric strength, which is the maximum value of the electric field that it can tolerate without breakdown. Several dielectric strengths are listed in Table A.2. Capacitors in Series and in Parallel. When there is a combination of capacitors in a circuit, sometimes we can replace the combination with a single capacitor with an Table A.2 Some Properties of Dielectrics (Insulators) Dielectric Dielectric Strength Material Constant (k)a (kV/mm) Air (1 atm) 1.00054 Polystyrene Paper Transformer oil Pyrex Ruby mica Porcelain Silicon Germanium Ethanol Water (20°C) Water (25°C) Titania ceramic Strontium titanate For a vacuum, K = unity. aMeasured at room temperature, except for the water. Source: Fundamentals of Physics - Extended, 4th ed., p. 751, Table 27-2. (Ref. 3, reprinted with permission.) A.7 INDUCTANCE AND CAPACITANCE Figure A.13 Capacitors in parallel. equivalent capacitance value. Just as resistances and inductances can be in series and in parallel, we can have capacitors in series and in parallel. Figure A.13 shows several capacitors in parallel. As we see in the figure, each capacitor has the same potential difference across its plates (i.e., the b