The power relationship on a transformer states that __________.

• A. Power in = power out + loss
• B. Power in = Power out
• C. Power in = Power out - Loss
• D. Power in = Loss

Answer: (A)

Power input to a transformer equals what is delivered to the load plus the losses inside the transformer. In an ideal transformer there are no losses, so input power would equal output power. In real equipment, losses come from winding resistance (copper losses), magnetic core losses (hysteresis and eddy currents), and other stray losses. This means the actual relationship is input power = output power + total losses. For example, if you push 1000 W into the transformer and it has 25 W of losses, the load side would receive 975 W. The other options imply no losses, or misplace the loss term, which doesn’t reflect how transformers actually operate.