The thermometer whose reading is indicated by a change in colour of its thermometric property is the?

A. bi-metallic strip thermometer
B. thermocouple
C. platinum resistance thermometer
D. optical pyrometer

Correct Answer:

Option D – optical pyrometer

Explanation

A pyrometer is an instrument for measuring high temperatures.
The optical pyrometer is one in which the luminous radiation from the hot body is compared with that from a known source.