* Referring to your printed notes; either copy these notes or annotate your printed notes

Reactance

The term reactance (X) is the opposition to the flow of ac currents. As we have seen in the Higher course, for a resistor the opposition to current in dc and ac is the same. However we have seen how for both capacitors and inductors the opposition to current in ac varies with frequency and differs from that in dc.


For the aside below refer to the wave equations learned in the Quanta and Waves section: 
"y = Asin(2πft)"


From the expression of reactance, XL, is measured in ohms when V is in volts and I is in amperes. 

The peak current is Ipk and Vpk = 2πfLIpk. From that, the inductor’s reactance is worked out as: 

So:
 For a Capacitor
(Capacitive Reactance)
 For an Inductor
(Inductive Reactance)