Answer: (A) Core Losses
Explanation:
Iron loss is caused by the alternating flux in the core and consists of hysteresis and eddy current losses. These losses occur in the core and yoke due to alternating flux. Copper losses occur in the primary and secondary windings due to their resistances when the transformer is loaded. Iron losses ( core losses ) are independent of load and therefore are called constant losses. Generally at maximum efficiency, the core loss of the transformer is equal to the copper loss. Again the transformers are so designed that the maximum efficiency of the transformer reaches a full load current. So for all other load copper loss is less than core loss hence core loss dose have maximum value among all other losses in a power transformer and that is why the efficiency of a transformer mainly depends upon core losses.