Physics Paper 3 WASSCE (SC), 2018

Alternative A

 

Question 3A

 

 

You are provided with an ammeter, resistor, key, metre bridge and other necessary apparatus.
(i)  Connect a circuit as shown in the diagram above.
(ii)   Close the key and use the jockey to make contact with AB at N such that AN = d = 25 cm.
(iii)  Read and record the ammeter reading I.
(iv)  Evaluate I-1
(v)  Repeat the procedure for values of d = 35 cm, 50 cm, 65 cm, and 80 cm.  In each case, record I and determine I-1
(vi)  Tabulate your results.
(vii)  Plot a graph with I-1 on the vertical axis and d on the horizontal axis.
(viii) Determine the slope, s, of the graph.
(ix)  State two precautions taken to obtain accurate results.

(b)  (i)        Use the graph to determine the value of d =I =1.5 A.
(ii)  State two factors which affects the resistance of a wire.

 

Observation

 

 

Part (a) Performance was poor. Many candidates who attempted this question failed short in so many ways. Candidates were unable to record d to at least 1 d.p in cm, I to at least 1 d.p in A and evaluation of I-1 and log I-1 to 3 s.f each.
Part (b) Candidates responded unsatisfactorily. Many candidates were unable to determine the value of I = 1.5 A.

The expected response:

  • Five values of d correctly read and recorded to at least 1 d.p in cm                                                                                                          
  • Five values of I correctly read and recorded to at least 1 d.p in A                
  • Five values of I-1 correctly evaluated to at least 3 s.f.  
  • (Five values of log I-1 correctly evaluated to 3 s.f 
  • Composite table showing at least d, I, I-1 and log I-1
  • Both axes correctly distinguished     
  • Plot a graph using reasonable scales 
  • Draw line of best fit
  • Determine the slope of the graph
  • State any two of the following precautions.

e.g.

  • Key opened in between readings/key opened when readings were not taken
  • Tight connections ensured
  • Avoided parallax error when taking reading on ammeter/metre rule
  • Repeated readings shown
  • Avoided/Noted/corrected zero error on ammeter/metre rule
  • Clean terminals ensured
  • Avoided dragging jockey on the potentiometer