CET AC Circuit Analysis & Power 2

Question 1

In a series RLC circuit at resonance, which statement is TRUE?

Accepted Answer

Inductive and capacitive reactances are equal and cancel

Answer

At resonance, XL = XC, so they cancel, leaving only resistance in the circuit.

Question 2

What is the phase relationship between voltage and current in a purely capacitive AC circuit?

Accepted Answer

Current leads voltage by 90°

Answer

In a purely capacitive circuit, current leads voltage by 90° (ELI the ICE man mnemonic — I before E in C).

Question 3

A circuit has a true power of 300 W and an apparent power of 500 VA. What is the reactive power?

Accepted Answer

400 VAR

Answer

Reactive power Q = √(S² − P²) = √(500² − 300²) = √(250000 − 90000) = √160000 = 400 VAR.

Question 4

Which instrument is used to measure the phase angle between voltage and current in an AC circuit?

Accepted Answer

Power factor meter

Answer

A power factor meter directly measures the cosine of the phase angle (power factor) between voltage and current.

Question 5

What happens to the capacitive reactance (XC) of a capacitor if the frequency of the applied AC signal is doubled?

Accepted Answer

XC is halved

Answer

Since XC = 1/(2πfC), doubling frequency halves the capacitive reactance.

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