Applications of bimetal strips: identify where bimetal strips are not used among the listed devices and controls.

Introduction / Context:Bimetal strips exploit the different thermal expansion coefficients of two bonded metals; when heated, they bend. This simple principle is used for temperature indication and on–off switching in numerous devices. Thermocouples, in contrast, rely on a thermoelectric effect and do not use bimetal bending.

Given Data / Assumptions:

• Bimetallic behavior: differential expansion causes deflection.
• Thermocouple behavior: Seebeck effect generates a millivolt signal at a junction of dissimilar metals.
• Devices listed include both thermal-mechanical and electro-thermoelectric types.

Concept / Approach:Bimetallic thermometers and thermostats directly use the bending of a bimetal strip. Relays and cut-outs often include bimetal elements to actuate electrical contacts with temperature. A thermocouple, however, contains no moving bimetal element; it is a junction producing EMF proportional to temperature difference.

Step-by-Step Solution:

Verification / Alternative check:Instrument catalogs clearly distinguish bimetal thermometers/thermostats (mechanical) from thermocouples (electrical EMF sensors).

Why Other Options Are Wrong:

Common Pitfalls:Assuming any “two metals” device is bimetallic; thermocouples use two metals but for Seebeck voltage, not bending.

Final Answer:Thermocouples