Most modern transformers are ____ efficient.

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Transformers waste only a small portion of the power they transfer, so their efficiency is very high. Efficiency is output power divided by input power, and the losses that reduce efficiency come from two main sources: core losses in the magnetic material (which stay roughly constant with voltage) and copper losses in the windings (which rise with current). Modern transformers use better magnetic materials, tighter winding designs, and improved cooling to minimize these losses. That combination typically places full-load efficiency in the mid-to-high 90s, commonly around 97–99%. The range 96–99% best reflects real-world performance for most modern transformers. The other options either underestimate typical performance or assume almost perfect efficiency, which isn’t achievable due to those unavoidable losses.