Physics (Essay) Paper 2 WASSCE (SC), 2023

Question 6

 

  1. State one difference between an intrinsic and an extrinsic semiconductor.
  2. 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


capacitor
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