Question

For a parallel RLC circuit, the incorrect statement among the following is _____________

(a) The bandwidth of the circuit decreases if R is increased

(b) The bandwidth of the circuit remains same if L is increased

(c) At resonance, input impedance is a real quantity

(d) At resonance, the magnitude of input impedance attains its minimum value

I got this question in a national level competition.

Asked question is from Problems of Parallel Resonance Involving Quality Factor topic in division Resonance & Magnetically Coupled Circuit of Network Theory

Answer 1

The correct choice is (d) At resonance, the magnitude of input impedance attains its minimum value

The explanation is: BW = 1/RC

It is clear that the bandwidth of a parallel RLC circuit is independent of L and decreases if R is increased.

At resonance, imaginary part of input impedance is zero. Hence, at resonance input impedance is a real quantity.

In parallel RLC circuit, the admittance is minimum, at resonance. Hence the magnitude of input impedance attains its maximum value at resonance.