AC Theory: RLC Circuits & Resonance is one of 9 topics in the Grade 12 Electrical Technology CAPS syllabus, covered across 3 lessons on Study Vault. Below are real practice questions from this topic with full worked answers.
Sample practice questions
Easy
1. Which formula correctly calculates inductive reactance (XL)?
XL = 2 x pi x f x L
XL = 1 / (2 x pi x f x C)
XL = R + L
XL = V / I only
Answer: XL = 2 x pi x f x L — Inductive reactance is calculated as XL = 2*pi*f*L, where f is frequency in hertz and L is inductance in henries.
Easy
2. In a purely inductive AC circuit, what is the phase relationship between current and voltage?
Current lags voltage by 90 degrees
Current leads voltage by 90 degrees
Current and voltage are perfectly in phase
There is no phase relationship in an inductive circuit
Answer: Current lags voltage by 90 degrees — In a purely inductive circuit, current lags voltage by 90 degrees, since an inductor opposes a change in current.
Medium
3. Calculate the inductive reactance, in ohms, of a 0,2 H inductor at a frequency of 50 Hz. Use XL = 2*pi*f*L and round to the nearest whole number.
Answer: 63 — XL = 2 x pi x 50 x 0,2 = 62,83, which rounds to 63 ohms.
