WAEC Physics 2023 Theory — Question 6

Model answer

(a) Intrinsic semiconductors are pure semiconductors with no impurities, have an equal number of charge carriers (holes and electrons), and have low electrical conductivity (high resistivity). Extrinsic semiconductors contain impurities (are doped), have an unequal number of charge carriers, have high electrical conductivity (low resistivity), and the charge carriers are thermally generated (intrinsic) versus resulting from doping (extrinsic). (b) A full-wave smoothing rectification circuit consists of an AC input connected through diodes (D1, D2 in a bridge or centre-tap arrangement) to a smoothing capacitor (C) in parallel with the load resistor (RL). The diodes rectify (remove the negative component of) the input voltage and convert it into pulsed DC, which is then smoothed by the capacitor to produce a nearly steady DC output signal.