Applied example — three resistors of 5 Ω, 10 Ω, and 20 Ω are connected in series. Is the total (equivalent) resistance equal to 35 Ω under ideal conditions?

Introduction / Context:
Concrete numerical examples reinforce the series-resistance rule. Here, you are asked to validate a straightforward calculation for three resistors connected in series. Such checks are essential when sizing supplies and estimating current and power distribution in a chain.

Given Data / Assumptions:

• Resistors: 5 Ω, 10 Ω, 20 Ω.
• Series connection (single current path).
• Ideal components; ignore tolerance and temperature coefficients.

Concept / Approach:
The series combination rule says: R_total = R1 + R2 + R3. Since the current is common to all three, the voltage drops add to the source voltage, and the resistances add arithmetically to give the equivalent seen by the source. No reciprocals are used for series addition; those apply to parallel networks.

Step-by-Step Solution:

Verification / Alternative check:
Measure with an ohmmeter across the three in series. Within tolerance, the reading will approach 35 Ω. Any deviation comes from component tolerances and lead/contact resistances, not from the combination rule.

Why Other Options Are Wrong:

• Incorrect: Conflicts with the series sum rule.
• Correct only at 25 °C: Temperature affects value slightly but not the arithmetic rule.
• Series uses reciprocals: Reciprocals are for parallel, not series.

Common Pitfalls:
Accidentally applying the parallel formula to a series problem or overlooking unit symbols (Ω vs kΩ) when summing values.

Final Answer:
Correct — 5 Ω + 10 Ω + 20 Ω = 35 Ω in series.