The strength of an electromagnet is primarily proportional to its diameter.

• A. False
• B. True
• C. Sometimes
• D. Not at all

Answer: (A)

The thing that determines how strong an electromagnet is comes from how much current you push through and how many turns you have, along with the core material. Those ampere-turns and the core’s permeability set the magnetic field density inside the coil.

If you keep the current and the number of turns fixed but make the coil bigger in diameter, the field density (the strength per unit area) stays about the same. What changes is the total flux you can pass through a given area: flux scales with the cross-sectional area, so a larger diameter lets more total flux flow, but the field strength itself isn’t primarily increased by the diameter. To make the magnet stronger, you’d increase current, add more turns, or use a core with higher permeability.

So the statement that strength is primarily proportional to diameter isn’t correct.