JAMB Physics 2015 Paper

Concept:The strength of an electromagnet depends on the number of turns of the coil and the current through the coil.Explanation:The magnetic field strength of an electromagnet is given by $B = \mu_0 n I$, where $n$ is the number of turns per unit length and $I$ is the current.Therefore, increasing the number of turns of the coil increases the strength of the electromagnet.Increasing the current also increases the strength, but option D says “without the coil,” which is incorrect.Answer:A. Increases in the number of turn of the coil