The opposition offered to an alternating current in a C-R series circuit is known as

Analyze the question: It asks for the name of the total opposition to alternating current in a series circuit containing a capacitor (C) and a resistor (R).

Explain the concept:

• Resistance (R): opposition to current from the resistor. It is the same for AC and DC and has no phase effect.
• Reactance (X): opposition from a capacitor or inductor only. For a capacitor, X_C = 1/(2πfC).
• Impedance (Z): the combined opposition of resistance and reactance in an AC circuit.
• Friction: a mechanical force, not an electrical term.

Solution: In a C-R series circuit, the resistor and the capacitor both oppose the current. Because the voltage across R and the voltage across C are 90° out of phase, we cannot simply add R and X_C. We combine them like the sides of a right-angled triangle:

Z = √(R² + X_C²)

where X_C = 1/(2πfC).

So the overall opposition to the alternating current in the circuit is the impedance, measured in ohms (Ω).

Checking the options:

• A. Impedance: correct, since it is the total opposition from R and C together.
• B. Resistance: only the resistor's part.
• C. Reactance: only the capacitor's part.
• D. Friction: not an electrical term.

Exam tip: Remember "Z is the Zum total." Impedance (Z) = the whole opposition, made up of R and X. Whenever a question says "series circuit" with both a resistor and a capacitor or inductor, think impedance. If it names only a capacitor or inductor, think reactance.