Which point on Figure E5-1 best represents the impedance of a series circuit consisting of a 300-ohm resistor and a 19-picofarad capacitor at 21.200 MHz?

Answer: A. Point 1

XC = 1 / (2 pi f C) = 1 / (2 x 3.1416 x 21.2e6 x 19e-12) = about 395 ohms. The impedance is 300 - j395, which is 300 to the right and about 400 down: Point 1.

Tip: Capacitive points plot below the axis.