Which material is the most popular for the windings?

• A. Copper
• B. Aluminum
• C. Gold
• D. Silver

Answer: (A)

Windings are chosen for low resistance, good ductility to make many turns, and practical cost. Copper offers excellent electrical conductivity—among widely used metals, only silver is a bit better, but copper hits a very favorable balance with much lower cost. It can be drawn into thin wires and wound tightly around cores, and it works well with insulation and manufacturing processes. Its thermal conductivity also helps carry away heat from the winding, improving reliability. Aluminum is lighter and cheaper, but its higher resistivity means you need larger cross-sections to get the same performance, and its oxide layer can complicate connections. Silver would minimize losses further, but its price makes it impractical for most windings, and gold is far too costly for everyday use. So copper is the most popular choice.