
Ill
necessary driving
e.m.f.
And since reactance is equal to applied
voltage divided by current (the same in both cases) it follows that the
total reactance of the circuit is also equal to one of the separate
reactances less the other.
Which voltage or reactance must be subtracted from which to give
the total? There is no particular reason for favouring either, but the
agreed convention is to call X
L
positive and negative.
For example, suppose L in Fig. 8.1 is 2 H, C is 2μΡ, and ab is
240 V at 50 Hz. We have already calculated the reactances of 2 Η
and 2μΡ at 50 Hz (Sees. 7.2 and end of 6.3) and found them to be
628 Ω and 1592 Ω. So the tota ...