DOUBLE-SUBSCRIPT NOTATION

An alternating quantity is generally represented by a double-subscript notation. In this notation, two letters are placed at the foot of the symbol for voltage or current, as shown in Figure 8.2. This conveys the following two scenarios:

1. The subscript of the symbol for voltage or current indicates the portion of the circuit where the quantity is located.
2. The order of the subscript indicates the positive direction of the quantity in which it acts.

Fig. 8.2  Circuit to represent double subscript notation

For instant, the current is represented as I_ab. It means that

1. The portion ab of the circuit is considered.
2. The current flows from a to b.

The double-subscript notation is very useful in solving AC circuits having a number of voltages and currents.