In an electromagnet, what happens if you increase the number of turns on the coil while keeping the current the same?

• A. Decrease magnetic field
• B. No effect
• C. Change material
• D. Increase magnetic field

Answer: (D)

More turns with the current held constant increase the magnetomotive force, which strengthens the magnetic field inside the electromagnet. The magnetic field in a coil is tied to the product of the number of turns and the current (N·I); with the same current, adding turns raises this product, boosting flux in the core. In a typical solenoid with a core, B is proportional to μ0·μr·N·I divided by the length, so increasing N directly increases B (at least until the core saturates). The other possibilities don’t fit because they’d require changing the current, the coil length, or the material, none of which is happening here.