Final answer:
As the nail used in an electromagnet increases in size, more magnetic domains can align, which typically results in an increase in the strength of the electromagnet.
Step-by-step explanation:
When considering the effect of increasing the size of a nail used in an electromagnet, we need to think about the number of magnetic domains that can be aligned in the material when a current is passed through a coil surrounding the nail. As the size of the nail increases, there is more material for the magnetic domains to align which typically means that the strength of the electromagnet increases as well. Hence, the correct answer to the question is (c) It will increase.
Magnetic fields, just like electric fields, decrease in strength as the distance from the source increases. This behavior is indeed consistent with our experience with magnets, where the force of attraction or repulsion between two magnets is felt strongly when they are close together and weakens as they are moved further apart.