waecE-LEARNING
Physics Paper 3, May/June 2014  
Questions: 1 2 3 Main
General Comments
Weakness/Remedies
Strength

 

 

 

 

 

































 

Question3

  

 

(a)

You are provided with a potentiometer AB, a 10Ω standard resistor R, a battery of emf 4.5 V, a jockey J and other necessary materials.        

  1. Connect a circuit as shown in the diagram above.
  2. Close key K.  Without J making contact with AB, read and record the ammeter reading I.  Open the key.
  3. Use the jockey to make contact with AB at the 20 cm mark such that AJ = x = 20 cm.   Close the key, read and record the ammeter reading Ii.                                                             

(vi)    Evaluate x -1.
            (v)     Repeat the procedure for values of x = 35 cm, 45 cm, 60 cm and 80 cm respectively
            (vi)    Tabulate your readings

  1. Plot a graph with x -1 on the vertical axis and Ii on the horizontal axis, starting both axes from the origin (0,0).
  2. Determine the slope, s, of the graph.
  3. From your graph, determine the value Io of Ii for which x -1 = 0.
  4. Evaluate .
  5. State two precautions taken to obtain accurate results.

(b)        (i)         Define emf of a battery.
(ii)        A cell X of emf 1.018 V is balanced by a length of 50.0 cm on a potentiometer wire.  Another cell Y is balanced by a length of 75.0 cm on the same wire.  Calculate the emf of Y.

 

  


_____________________________________________________________________________________________________
Observation
Part (a)   This was another popular question among the candidates.  Many candidates did not record the initial ammeter reading I while few others interchanged the values of I for Io while evaluating .   The determination of Io for which x -1 = 0 was poor handled.  Those candidates that handled it evaluation correctly failed to record the answer to the appropriate number of decimal places.  Generally performance was average.

 

Part (b)

  • Was well handled by most responding candidates while most candidates  could not do justice to numeral (ii).  Most of the candidates could not give the correct formula.

Candidates are expected to:

    

  •  Read and record value of ammeter reading I to at least 1 d.p  in amperes.
  •  Correctly record five values of x to at least 1 d.p in cm.

 (iii)         Read and record five values of Ii to at least 1 d.p  in amperes
                                       and in trend 
                                       Trend:  As  increases,  decreases                                                               
                       (iv)           Correctly evaluate five values of x –1 to at least 3 d.p.                                                      
           (v)            Show composite table containing , x, and     

  • Plot graph using reasonable scales
  • Draw line of best fit
  • Determine the slope of the graph
  • Evaluate  Io for which x -1 = 0 and     
  • State two of the following precautions. 

 

       e.g  -   Ensured tight connections/clean terminals.
                     -   Key removed when not taking readings
                     -   parallax error avoided in reading ammeter/metre rule
                     -   Avoided sliding the jockey on the potentiometer wire/jockey not allowed
                         to scratch the wire

  • Zero error noted and corrected/avoided on ammeter/ metre rule
  • Repeated readings shown on table.

In part (b), the expected answers are:

       (b)(i)     The emf of a battery is  the work done in joules in conveying one coulombs
                     of charge round a complete circuit
 
          (ii)          =                                                                                     

                         =                                                                                 

                        Ey   =    1.527V                                


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