During troubleshooting of a prototype wearable device, engineers observe intermittent dimming of an indicator LED powered by a compact battery pack. The simplified single-loop circuit contains the battery pack, a ON/OFF switch, a series current-limiting resistor, and the LED module. To diagnose the problem, an engineer measures steady-state potential differences at several points immediately after a dim event and records the following values (positive probe first):
• Battery terminals: +5.0V
• Across the switch (closed position): −0.8V
• Across the current-limiting resistor: −2.4V
• Across the LED module: −1.6V
• Between two nodes on the same copper trace, 1 cm apart: −0.7V
The normal operating current of the circuit is approximately I=120mA.
(a) Using the measured data, determine whether the circuit satisfies energy conservation at the moment of measurement. Show quantitative evidence.
(b) Identify which segment of the circuit is most likely responsible for the unexpected potential drop and explain your reasoning.
(c) Design a step-by-step measurement plan, using only a digital voltmeter, that would allow a technician to locate and quantify the resistance of the suspect connection without interrupting normal operation more than once.
(d) Calculate the maximum additional resistance that the suspect connection may have before the algebraic sum of potential differences violates energy conservation by more than ±0.1V under the stated operating current. Express your answer in ohms to two significant figures.