Reliability of variable resistors (potentiometers and rheostats): Consider the maintenance issue: “Variable resistors often develop problems with the wiper making reliable contact with the resistive track.” Evaluate this statement.

Introduction / Context:
Variable resistors—potentiometers and rheostats—use a sliding wiper that contacts a resistive element. Over time, environmental contaminants, wear, and oxidation can degrade that contact, leading to noisy or intermittent operation. Recognizing this common failure mode is helpful in troubleshooting audio equipment, controls, and instrumentation.

Given Data / Assumptions:

• Devices considered: carbon composition, cermet, conductive plastic, and wirewound potentiometers.
• Operating in typical lab or field environments.
• No special hermetic sealing unless specified.

Concept / Approach:
The wiper-to-track interface is a mechanical contact subject to friction and contamination. Dust, smoke, and moisture can infiltrate the housing, while mechanical wear creates debris. Oxidation films increase contact resistance and create scratching or “crackling” noise in audio paths. Even in wirewound types with robust windings, the wiper junction can degrade. Hence wiper contact issues are a well-known reliability concern for variable resistors.

Step-by-Step Solution:

Verification / Alternative check:
Maintenance practices include contact cleaning sprays, exercising the pot, or replacing with sealed or digital (encoder plus DAC) alternatives—evidence that wiper contact reliability is a known issue manufacturers mitigate in datasheets and application notes.

Why Other Options Are Wrong:

• Incorrect: Contradicts common field experience.
• Only true for wirewound / above 1 A / sealed enclosures: Contact problems can occur across types and at small signal levels; sealing helps but does not eliminate wear.

Common Pitfalls:
Assuming that increasing contact pressure always helps (it can accelerate wear), and overlooking that DC across the wiper can create micro-arcing and residue, worsening noise.

Final Answer:
Correct