Question

Suppose you have an RLC series circuit constructed using a resistor with a non-zero resistance, an inductor with non-zero inductance, a capacitor with non-zero capacitance, and for which the voltage lags the current. How could you get this circuit to resonance by varying only the capacitance of the capacitor (it’s a variable capacitor)?

Group of answer choices

a) Decrease the capacitance of the capacitor.

b) Increase the capacitance of the capacitor.

c) Actually, only varying the capacitance of the capacitor cannot get the circuit to resonance.

Answer 1

In Series LCR circuit, phase angle between Current and voltage is given by

where XC is capacitive reactance, XL is inductive reactance and R is resistance.

when XC > XL , phase angle is positive, Current leads voltage or voltage lags behind current.

Since we are given that voltage lags behind current, capacitive reactance is greater than inductive reactance.

To get resosnance we need to make XC and XL equal , i.e. we need to decrease XC .

Capacitive reactance XC = 1/( C )

Hence to decrease XC , capacitance should be increased