A piece of stone with its volume 400 cm cube and density 7.8 into 10 to the power 3 kg per metre cube is totally immersed in water of density 1000 kg metre cube calculate the weight of the stones in air and upthrust of water​

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.