A student writes an expression for the momentum (p) of a body of mass (m) with total energy (E) and considering the duration of time (t) as p = V2 m Elt. Check its correctness on dimensional analysis.

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.