It takes a thermocouple 15 seconds to reach the temperature

It takes a thermocouple 1.5 seconds to reach the temperature change equal to 99% of the difference between its initial and final equilibrium temperature. The time constant of the thermocouple must be: less than 1.5 seconds. Equal to 1.5 seconds. greater than 1.5 seconds. cannot be calculated from the information given.

Solution

The “Time Constant” or “Response TIme” is defined as the time required to reach 63.2% of an instantaneous temperature change

so for 99% it took 1.5 seconds then for 63.2% it will be less than 1.5 seconds