What is a disadvantage of a bimetal thermostat when compared to an electronic thermostat?

• A. More expensive
• B. Not precise
• C. Requires more maintenance
• D. Works only with direct current

Answer: (B)

The main idea is that bimetal thermostats rely on a mechanical mechanism whose actuation point drifts over time, making them less precise than electronic controls. A bimetal strip is made of two metals with different expansion rates; as temperature changes, the strip bends and trips a switch. That bending response isn’t perfectly at a fixed temperature—it's influenced by ambient conditions, how quickly temperature changes, mounting, and wear from cycling. Over time the materials age and the contact can shift, so the actual temperature at which it turns on or off drifts. All of this leads to less repeatable and less exact temperature control.

Electronic thermostats, by contrast, use a sensor and digital processing to decide when to switch, plus calibration and consistent sensing, which yields tighter, repeatable setpoints with minimal drift. That contrast is why precision is the standout disadvantage of the bimetal option.

As for the other points, these devices are typically cheaper, not more expensive, and they don’t require heavy maintenance. They’re designed to switch the circuit regardless of whether the load is AC or DC, so they aren’t limited to direct current.