Question

A common pickup for an electric guitar consists of a coil of wire around a small permanent magnet, as described in Figure 25.5. Why will this type of pickup fail with nylon strings?

Answer 1

Guitar pickups are tiny coils with magnets inside them and they work via  the principal of electromagnetic inductance. The metal strings vibrate within the magnetic field of the pickup which generates an electrical current. Since nylon is not a metal, it will not cause fluctuations in that magnetic field. Hope this answer helps.