Auto Electrical Works Paper 2, WASSCE (SC), 2022

Question 1                                                                                                                                                  
(a)        State one function of:

  • a battery in the operation of a motor vehicle;
  • an electrolyte in a battery.

            (b)        (i) State two factors that affect the capacity of a lead acid battery. 
(ii) A lead acid battery delivers a current of 0.5 A steadily for 120 hours. Calculate the
capacity of the battery.                
            (c)        Table 1 contains some components of a lead acid battery. Complete it by giving one
material used in making each of the parts listed.                                                     
                                                                       Table 1


S/N

Component part

Material used

(i)

Positive plate

 

(ii)

Negative plate

 

(iii)

Separator

 

(iv)

Casing

 

(v)

Cell connectors

 

                        Complete Table 1 by stating one symptom of fault and one remedy for each fault listed.

 

The expected responses were:

  • (i)        Function of a battery in the operation of a motor vehicle
  • to supply  the necessary current to the starter motor and ignition system while

cranking to start the engine

  • to supply additional current when the demand is higher that the alternator can supply
  • acts as electrical reservoir for current supply when necessary

                                                                                                                     

(ii)       Function of an electrolyte in a battery

  • break down to cause the movement of ions which results in the flow of current.
  • Serves as catalyst to make the battery conductive by promoting the movement of ions from the cathode to the anode and is reserve on discharge
  • Stores chemical energy to be converted into electrical energy.
  •  (i)   Factors that affect the capacity of a lead acid battery
  • surface area of electrode
  • plate surface area
  • number of plates
  • strength of electrode
  • operating temperature
  • age of battery
  • rate of discharge                                                                                                                                                                             

(ii)  Calculation
capacity = current x time
= 0.5 x 120
= 60 Ah                                                                                                

 

  •                                                              Table 1

S/N

Component parts

Material used

(i)

Positive plate

lead oxide

(ii)

Negative plate

Spongy lead

(iii)

Separator

treated wood/plastic/hard rubber

(iv)

Casting

ebonite/plastic/hard rubber

(v)

Cell connectors

lead

                                                                                                         

                                                                                                                                               
Question 1 required candidates to show understanding of basic terminology of the battery and total output of a battery. More so, other part of the question required candidates to show familiarity with the component parts of a lead acid battery. The Chief Examiner reported that majority of the candidates that attempted question 1 could neither show understanding of the materials component parts of batteries are made of  nor state the factors that affect the capacity of a  lead acid battery.