why power is constant in transformer?

Power remains constant in a transformer due to the principle of conservation of energy. In an ideal transformer, the input power (primary side) equals the output power (secondary side), minus any losses. This means that the product of voltage and current on the primary side equals the product of voltage and current on the secondary side (P_primary = P_secondary). Therefore, while voltage and current may change, the overall power remains constant, ensuring efficient energy transfer.