Heat and Mass Transfer
The thermal diffusivities for gases are generally

Less than those for liquids
More than those for liquids
Dependent on the viscosity
More than those for solids

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Heat and Mass Transfer
The time constant of a thermocouple is

The time taken to attain the final temperature to be measured
The time taken to attain 50% of the value of initial temperature difference
Determined by the time taken to reach 100°C from 0°C
The time taken to attain 63.2% of the value of initial temperature difference

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