Deck 9: Parallel A.C Circuits

Question 1

Decide whether each of these statements is True (T) or False
An a.c. circuit has a pure resistor in parallel with a pure inductor.
(i) The current through the inductor lags behind the supply voltage by 90º.
(ii) The current through the resistor is in phase with the supply voltage.

A) (i) T (ii) T
B) (i) T (ii) F
C) (i) F (ii) T
D) (i) F (ii) F

Answer 1

A

Question 2

Decide whether each of these statements is True (T) or False
An a.c. circuit has a pure resistor in parallel with a pure capacitor.
(i) The current through the capacitor lags behind the supply voltage by 90º.
(ii) The current through the resistor is in phase with the supply voltage.

A) (i) T (ii) T
B) (i) T (ii) F
C) (i) F (ii) T
D) (i) F (ii) F

Answer 2

C

Question 3

Decide whether each of these statements is True (T) or False
An a.c. circuit has a coil, with resistance and inductance, in parallel with a capacitor. At resonance:
(i) The circuit presents a purely resistive load.
(ii) The circuit current and voltage are 90º out-of-phase.

A) (i) T (ii) T
B) (i) T (ii) F
C) (i) F (ii) T
D) (i) F (ii) F

Answer 3

B

Question 4

An a.c. circuit has a coil, with resistance 10 Ω and inductance 100 mH, in parallel with a capacitor and has a resonant frequency of 120 Hz. The Q-factor of the circuit is:

A) 0.01
B) 0.08
C) 0.13
D) 7.5

Question 5

For a parallel a.c. circuit with a supply voltage of 240 V r.m.s. and current 2.5 A r.m.s., the power factor is 0.9. The true power is:

A) 600 W
B) 540 W
C) 262 W
D) 0 W