2. Light from a helium-neon (I=633nm) illuminates two 0.40 apart. A viewing screen is 2.0 behind the slits. What are the distances between the two m = 3 bright fringes and between the two m = 3 dark fringes?

the answer is the first electromagnet (a). this is because it has more coils around the ferromagnetic material. increasing the number of coils increases the surface area in which the metal interacts with the current in the coil. this enables more atoms in the metal to become aligned hence becoming more magnetized.