27 A battery of e. m.f 8 volts and internal resistance 1 Ohm is connected
to a straight wire of length 10 cm, of cross sectional area 3 x 10-8 m² and its resis-
tivity 4.5 x 10-6 12. m. calculate the magnetic flux density at a point which lies at
normal distance 20 cm away from the center of the wire. d Lase

does anyone know or what?

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.