Auto Electrical Works Paper 3, WASSCE (SC), 2019

Question 3

 

AIM: To test candidates’ knowledge of a motor vehicle lighting system

.

           

     

  1.       Connect the circuit as shown in Fig. 2

    .

  2.    

  3.       Ask the supervisor to check the circuit connection.


  4.   

  5.       Close the switch to point Y and start the stopwatch simultaneously.


  6.  

  7.  
           Record in Table 4:


           

    1.      your observation as either ON or OFF.>


    2.      

    3.      the number of flashes in 10 seconds in the column for n1.


  8. Table 4          

    Test

    Condition of switch

    L

    R

    LF

    LR

    RF

    RR

    No. of flashes
    n1

    No. of flashes
    n2

    Avg. no. of flashes

    1.

    Switch closed to Y

     

     

     

     

     

     

     

     

     

    2.

    Switch closed to X

     

     

     

     

     

     

     

     

     

    3.

    Switch closed to X and bulb R removed

     

     

     

     

     

     

     

     

     

    4.

    Switch closed to Y and bulb LR removed

     

     

     

     

     

     

     

     

     

                    

  9.    Repeat step (d) (ii) and record the number of flashes in the column for n2


  10.    

  11.   Repeat steps (c) and (e) for the other tests in Table 4

    .

  12.    

  13.   Complete Table 4 by calculating the average number of flashes.


  14.  

  15.    Compare and comment on your results in:

    1.      

    2.    tests1 and 4


    3.       

    4.    tests2 and 3.


         

  16.    With all the bulbs in position, close the switch to Y and record the ammeter readings A1, A2 and A3.

  17.       

  18.   State the relationship between the ammeter readings in (i).


  19.    

  20.     Remove bulb LF read and record the ammeter readings A1, A2 and A3.

  21.                 

  22.      State the relationship between the ammeter readings in (k). 


  23.     

  24.   State the type of connection employed in Fig. 2.

  25.     

  26.    State one application of the circuit in Fig. 2 in a motor vehicle.


 

Observation

 

 

Table 4

 

Condition of switch

L

R

LF

LR

RF

RR

No. of flashes n1

No. of flashes n2

Avg. no of flashes

I.

Switch closed to Y

ON

OFF

ON

ON

OFF

OFF

15

16

15/16

II.

Switch closed to X

OFF

ON

OFF

OFF

ON

ON

16

16

16

III.

Switch closed to X and bulb R removed

OFF

__

OFF

OFF

ON

ON

16

16

16

IV.

Switch closed to Y and bulb LR  removed

ON

OFF

ON

__

OFF

OFF

35

35

35

 (h)       (i)         The bulbs that were ON in test 4 blinked faster than those that were ON in test 1  
(ii)        Bulbs that were ON in test 2 blinked at the same rate as those that were ON in test 3.

(i)         A1 = 3 A                                                                     
A2 = 2 A         
A1 = 1 A                                                                                                                     
(tolerance of + 0.2)

(l)         Relationship between the ammeter readings in (i)

A1 is the sum of A2 and A3.                                                                                       
(k)        A1 = 1.0 – 1.5 A                     
A2 = 0                                     
A3 = 1.0 – 1.5 A

(m)       Parallel connection    
                                                                                                 
(n)        Application of the circuit in Fig.2 in a motor vehicle


  • To indicate intending direction of motor vehicle/Trafficator light

  • To indicate that there is an hazard or emergency situation

Candidates were required to test the effect of additional load on the flashing rate of a motor vehicle flasher unit. According to
the Chief Examiners report, majority of the candidates that attempted question 2 responded well the tasks of completing the table but only
a few gave meaningful readings of ammeters 1, 2 and 3.