Heat and Mass Transfer
An electric cable of aluminium conductor (k = 240 W/mK) is to be insulated with rubber (k = 0.15 W/mK). The cable is to be located in air (h = 6 W/m²). The critical thickness of insulation will be

40 mm
160 mm
800 mm
25 mm

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Heat and Mass Transfer
The time constant of a thermocouple is

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

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