An engineer is designing a system to lift scrap iron in a recycling plant using an electromagnet attached to a crane. Describe how the electromagnet is constructed and explain how its magnetic field strength can be increased to lift heavier loads.

An electromagnet is a solenoid, i.e. a coil of insulated copper wire wound around a ferromagnetic iron core.

When electric current flows through the coil, it produces a magnetic field that is confined to the interior of the solenoid and is directed along the axis of the core.

The magnetic field strength (B) inside a long solenoid is proportional to the current (I) and the number of turns per unit length (n): B = μ₀ n I, where μ₀ is the permeability of free space.

Therefore, increasing the current through the coil directly increases B, allowing a stronger attraction of the scrap iron.

Increasing the number of turns of wire on the solenoid also raises B, because a larger n gives a stronger field for the same current.

Finally, the iron core concentrates the field lines; iron has a much higher permeability than air, so the core amplifies the field and the core itself becomes an induced magnet, adding to the overall magnetic force.