A helium balloon containing 12m³ of gas at a pressure of 120kPa is released into the air. Assuming that the temperature is constant, calculate the volume the balloon would have when the pressure inside the balloon has fallen to 40kPa. Answer in m³.

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.