Question 6
- State one difference between an intrinsic and an extrinsic semiconductor.
- Draw a circuit diagram to illustrate full-wave smoothing rectification.
Observation
Many candidates differentiated between intrinsic and extrinsic semiconductors correctly.
Only a few candidates answer (b) and it was executed poorly. It is necessary to provide candidates with more assistance in this particular aspect of Physics.
EXPECTED RESPONSES:
(a) Difference between intrinsic and extrinsic semiconductors
Intrinsic |
Extrinsic |
Pure |
Contains impurities /doped |
An equal number of charge carriers/holes and electrons |
Has majority and minority charge carriers/unequal number of charge carriers |
Low electrical conductivity/high resistivity |
High electrical conductivity/low resistivity |
Thermally generated charge carriers |
Charge carriers result from doping |
(b) Sketch of the circuit to show full wave smoothing rectification
D1 and D2 shown
Capacitor shown
NB: (i) Accept diode-bridge arrangement
(ii) Do not accept d.c. source
(iii) Score zero for missing a.c. source