Practice portal › Alternating Current › Resonance in Series LCR

The value of the Q-factor in an L-C-R (AC) series circuit is _______.

Asked in GSEB Board July 2016 · Power and bandwidth at resonance

• (1) dependent on the values of all the three components L, R and C
• (2) dependent on the frequency of the A.C. source
• (3) dependent only on the values of L and C
• (4) it may or may not depend on power factor

Step-by-step solution

Why the other options are wrong

• (2) Q=(ω₀L)/R uses the resonant frequency ω₀=1/(√LC), which is fixed by L and C. Changing the frequency of the source does not change Q.
• (3) Leaves out R. In Q=1/R√L/C the resistance sits in the denominator: the smaller R, the sharper the resonance.
• (4) Too vague to be true. Q=1/R√L/C is fixed once L, C and R are fixed, while the power factor changes with the source frequency.

Reading this solution needs no sign-in. You only sign in to practise against the clock and keep your progress.