Thermal conductivity of a material may be defined as the________________?

A. quantity of heat flowing in one second through one cm cube of material when opposite faces ^re maintained at a temperature difference of 1°C
B. quantity of heat flowing in one second through a slab of the material of area one cm square, thickness 1 cm when its faces differ in temperature by 1°C
C. heat conducted in unit time across unit area through unit thickness when a temperature difference of unity is maintained between opposite faces
D. all of the above
E. none of the above

The time constant of a thermocouple is_______________?

A. the time taken to attain the final temperature to be measured
B. the time taken to attain 50% of the value of initial temperature difference
C. the time taken to attain 63.2% of the value of initial temperature difference
D. determined by the time taken to reach 100°C from 0°C
E. none of the above