In the case of a refrigeration system undergoing an irreversible cycle, $$\oint {{{SQ} \over T}} $$ is _____________$$\left( { < 0/ = 0/ > 0} \right)$$

Consider a refrigerator and a heat pump working on the reversed Carnot cycle between the same temperature limits. Which of the following is correct?

Any thermodynamic cycle operating between two temperature limits is reversible if the product of efficiency when operating as a heat engine and the coefficient of performance when operating as a refrigeration is equal to $$1.$$

A reversible heat transfer demands: