Question 279: AC fundamentals

Question

When a capacitor is connected in series LR circuit, the alternating current flowing in the circuit

Accepted Answer

We are given an LR circuit (an
inductor & resistor in series
).
Now, a capacitor is connected in series with it, making it an
LCR series circuit
.
Analysis:
In an
LR circuit
, the impedance is
$   Z_{LR} = \sqrt{R^2 + (\omega L)^2}   $
If a capacitor is added in series, the impedance becomes:
$   Z_{LCR} = \sqrt{R^2 + \left(\omega L - \frac{1}{\omega C}ight)^2}   $
Clearly, the impedance
does not remain constant
; it depends on frequency and C.
If $\omega L = 	frac{1}{\omega C}$, i.e. the circuit is in resonance, the reactances cancel each other, so:
$   Z = R   $
This is
smaller
than the LR impedance $Z_{LR}$.
Therefore, the current in the circuit
increases
.
So in general, adding the capacitor provides a possibility of cancelling out some inductive reactance, thereby reducing impedance and
increasing the current
.
Ã¢ÂÂ Correct Answer:
Option B Ã¢ÂÂ increases

Answer

remains constant

Answer

increases

Answer

decreases

Answer

is zero

AC fundamentals

When a capacitor is connected in series LR circuit, the alternating current flowing in the circuit

Choose the correct answer: