Question

The reciprocal of the total effective resistance of LCR a.c. circuit is called

• A. Impedance
• B. Admittance
• C. Resistance
• D. Inductive and capacitive reactance

Hint:

Physics Tip: Conductance is reciprocal of resistance, admittance is reciprocal of impedance.

Answer 1

The Correct Option is B

Step 1: Understand LCR circuit opposition. In an a.c. LCR circuit, the total opposition offered to current is called impedance. It includes:
• Resistance $(R)$
• Inductive reactance $(X_L)$
• Capacitive reactance $(X_C)$ The effective impedance is written as: $$ Z=\sqrt{R^2+(X_L-X_C)^2} $$

Step 2: Meaning of reciprocal quantity. The reciprocal of impedance measures how easily current can flow through the circuit. This quantity is called admittance. $$ Y=\frac{1}{Z} $$ where $Y$ denotes admittance.

Step 3: Physical meaning. Higher admittance means easier flow of alternating current. Lower admittance means circuit opposes current more strongly.

Step 4: Check options.
• Impedance = total opposition, not reciprocal.
• Admittance = reciprocal of impedance.
• Resistance alone is only one part of circuit.
• Reactances are components, not reciprocal quantity.

Step 5: Conclusion. $$ \therefore \text{Correct option is (B) Admittance.} $$