WAEC Physics 2011 Theory — Question 32

Model answer

(i) The lamp is lit when the a.c supply is switched on because the changing magnetic flux in X induces a corresponding changing magnetic flux in Y, which induces current that lights up the bulb. (ii) The brightness increases when the distance between X and Y decreases because as the distance decreases, the flux density linking coil Y increases, thus increasing the e.m.f/voltage induced in Y and consequently the brightness of the lamp. (iii) The filament of the lamp glows brighter when a bundle of insulated iron wires is placed along the common axis of the coils because the insulated soft iron wires concentrate/increase the magnetic flux through coil Y, thus increasing the e.m.f in Y, making the filament of the lamp glow brighter.