Series-aiding sources — four 9 V batteries connected in series and aiding each other produce a total of 36 V. Is this description correct for ideal sources?

Introduction / Context:
Stacking voltage sources is a common way to reach higher supply rails in portable systems. When sources are connected “series-aiding,” their voltages add algebraically with the same polarity orientation. This question checks your understanding by using four identical 9 V batteries as an example.

Given Data / Assumptions:

• Four ideal 9 V sources.
• Series-aiding orientation (polarity aligned head-to-tail).
• Neglect internal resistance for the basic calculation.

Concept / Approach:
For ideal voltage sources connected in series, the net voltage equals the signed sum of individual voltages. “Aiding” means all polarities line up to produce a larger resultant. Therefore, 9 V + 9 V + 9 V + 9 V = 36 V. In practice, small internal resistances cause voltage sag under load, but the open-circuit sum remains 36 V and loaded values are close if currents are modest.

Step-by-Step Solution:

Verification / Alternative check:
Measure open-circuit with a DMM: approximately 36 V. Under load, compute V_load = 36 V − I * (Σ r_internal) to estimate any droop; for light loads the reading remains near 36 V.

Why Other Options Are Wrong:

• Incorrect: Opposes the fundamental series addition rule.
• Correct only if internal resistance is zero: Internal resistance affects load voltage, not the ideal series summation principle.
• Voltages never add: They do add algebraically when sources are in series.

Common Pitfalls:
Confusing series-aiding with series-opposing; reversing one cell flips the algebraic sum and reduces the total rather than increasing it.

Final Answer:
Correct — four 9 V sources in series-aiding give 36 V (ideal).