Ques. How may the capacity of a condenser, wire, or cable be tested?
Ans. This may be done by the aid of a standard condenser, trigger key, and an astatic or ballistic galvanometer.
In making the test, first obtain a "constant" by noting the deflection d, due to the discharge of the standard condenser after a charge of, say, 10 seconds from a given voltage. Then discharge the other condenser, wire, or cable through the galvanometer after 10 seconds charge, and note the deflection d'. The capacity C' of the latter is then
| d' | ||||
| C' | = | C | × | |
| d |
in which C is the capacity of the standard condenser.
Fig. 1,284.—Series or cascade connection of condensers. Unlike terminals are joined together as shown. The total capacity of such connection is equal to the reciprocal of the sum of the reciprocals of the several capacities, that is, C = 1 ÷ (1 / c + 1 / c' + 1 / c")
Ohmic Value of Capacity.—The capacity of an alternating current circuit is the measure of the amount of electricity held by it when its terminals are at unit difference of pressure. Every such circuit acts as a condenser.
If an alternating circuit, having no capacity, be opened, no current can be produced in it, but if there be capacity at the break, current may be produced as in fig. 1,286.