Question

For a given temperature difference, which of the following pairs will generate maximum thermo emf?

• A. lead-nickel
• B. iron-copper
• C. silver-gold
• D. antimony-bismuth

Answer 1

Answer: (D)

antimony-bismuth

For a given temperature difference, the direction of current(and thermoemf) in a thermocouple depends on the metal chosen. the thermoelectric series is used to predict the direction of current in given temperature range. Thermoelectric series is,
Selenium, Antimony, Iron, Cadmium, Zinc, Silver, Gold, Lead, Mercury, Copper, Platinum, Nickel, Bismuth.
The metals preceding lead are thermoelectrically negative and succeeding lead are thermoelectrically positive. also, for a given temperature difference, metals with larger separation (between metals) produces greater thermoemf. In the series Antimony and Bismuth are quite distant, hence thermoemf produced will be large as compared to other pair of metals.