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Process Control and Instrumentation - Engineering

Q1:

Working principle of bimetallic thermometers is difference in linear co-efficient of thermal expansion of two strips of different metals welded together. Which of the following has the maximum thermal co-efficient of linear expansion?

A Nickel

B Brass

C Chromel

D Invar

ANS:B - Brass

The working principle of bimetallic thermometers is based on the difference in the linear coefficients of thermal expansion of two strips of different metals welded together. Among the metals listed, the one with the maximum thermal coefficient of linear expansion is Brass. Here are the approximate coefficients of linear expansion for the metals mentioned:

  • Nickel: ~13 × 10⁻⁶ /°C
  • Brass: ~19 × 10⁻⁶ /°C
  • Chromel: ~18 × 10⁻⁶ /°C (Chromel is an alloy of nickel and chromium)
  • Invar: ~1.2 × 10⁻⁶ /°C (Invar is known for its very low coefficient of thermal expansion)
Therefore, Brass has the highest thermal coefficient of linear expansion among the options provided.