Observation

  This is a test of practical, and a compulsory question. Majority of the candidates responded to it. The performance was fair.
 
In part (a), majority of the candidates labelled the marked parts, and listed four applications of the cell. 
In part (b), majority of the candidates could not state the causes of the faults in d.c. generator.

The expected answers include:

4(a)(i)  -    Electrolyte/Sal ammoniac solution
-     Zinc plate/-ve electrode  
-     Carbon plate/+v electrode
-     Container  

      (ii)      E. M. F of Lechanche′ cell                     1.5V

               Defects of Lechanche′ cell
(iii)    I.    -   Polarization             
-    Local action  

            Methods of minimizing defects of Lechanche′ cell
II.    -    The zinc electrode should be coated with mercury  to minimize local action  
-    The carbon plate should be surrounded  with depolarizing agent 

           III    Disadvantages of Lechanche′ cell
-    has low voltage/incapable of supplying large current
-   it cannot be used continuously due to effect of polarization
-   cannot be recharged/irreversible
-   has high internal resistance
-   it is not portable in this form.
-    ageing/short life span/deteriorate faster                                                               

            IV   Application of Lechanche′ cell
-   used in bell circuits
-    calculator
-   railway signal/indicators
-   for controlling switch gear in sub-stations
-   telegraphy/telephone (do not accept mobile phone)
-   radio set.
-   torch
-   microphone
-   remote control
-   watch                                                                                                  
V      Instrument used for measuring specific gravity of Lechanche′ cell
hydrometer                                                                                                                

                   Causes of fault in d.c. generator

(b)