The heat current is written as Why don’t we written ?

The term represents the partial derivative of Q (or the amount of heat transfer) with respect to time, while represents the absolute derivative of Q with respect to time. The the amount of heat transfer (Q) depends not only on time but also on the factors such as the area of cross-section, temperature difference, etc. So, we cannot write it as a complete derivative of time only. Hence the better way of representation of heat current is as a partial derivative or in the given form, which is, .


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