RLC Circuits is one of 9 topics in the Grade 11 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 L)
XL = f x L
XL = 2 x pi x f / L
Answer: XL = 2 x pi x f x L — Inductive reactance is calculated using XL = 2 x pi x f x L, where f is supply frequency in hertz and L is inductance in henries.
Easy
2. As supply frequency increases, what happens to capacitive reactance, XC?
XC decreases
XC increases
XC stays exactly constant
XC becomes undefined at any frequency above 0 Hz
Answer: XC decreases — Capacitive reactance decreases as frequency increases, since XC = 1/(2 x pi x f x C), an inverse relationship with frequency.
Medium
3. Calculate the inductive reactance, XL, in ohms, of a 0,2 H inductor at a supply 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 = 62,8, which rounds to 63 ohms.
