When the number of turns of the coil is doubled, the magnetic induction line will also be doubled. The magnetic induction line magnetizes the iron core, and the magnetic field will be multiplied. And electromagnets
The attractive force is proportional to the square of the magnetic induction intensity, so the magnetic force of the electromagnet is proportional to the square of the number of coils.
The formula of magnetic induction intensity: B = uN × I/Le.
Where: n is the number of turns of the excitation coil; I is the excitation current (measured value), in a; Le is the effective magnetic circuit of the sample.
Length, in meters