Question

If the frequency of the AC current increases, then the impedance of the series R-C circuit will:
1. Increase
2. Decrease
3. Remain same
4. First increase then decrease

Answer 1

Correct Answer - Option 2 : Decrease

CONCEPT:

Impedance:

• Impedance is a combination of resistance and reactance. It is essentially everything that resists the flow of electrons within an electrical circuit.

Reactance

• It is basically the inertia against the motion of the electrons in an electrical circuit.

• There are two types of reactance:

  1. Capacitive reactance (XC) (Ohms is the unit)

  2. Inductive reactance (XL) (Ohms is the unit)

​CALCULATION:

• The impedance of the series R-C circuit is given as,

\(\Rightarrow Z=\sqrt{R^{2}+X_{c}^{2}}\)     -----(1)

Where R = resistance and X_c = capacitive reactance

• The capacitive reactance is given as,

\(\Rightarrow X_{C}=\frac{1}{2\pi fC}\)     -----(2)

Where f = frequency of AC current

• By equation 2 it is clear that when the frequency of the AC current increases, the capacitive reactance will decrease.
• And by equation 1 it is clear that when the value of X_c decreases, the value of impedance also decreases.
• So it is clear that when the frequency of the AC current increases, the value of impedance decreases.
• Hence, option 2 is correct.