Question

For a parallel RLC circuit, which one of the following statement is NOT correct?

• 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

Answer 1

The correct option is D At resonance, the magnitude of input impedance attains its minimum value

Characteristic equation for a parallel RLC circuit is
$s^2+\frac{1}{RC}s+\frac{1}{LC}=0$
where, Bandwidth$=\frac{1}{RC}$

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

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

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