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Applied Electricity 1, Nov/Dec 2008  
Questions:   1 2   Main
General Comments
Weakness/Remedies
Strength
































































Question 1

(a) Connect the circuit as shown in fig. 1 and set R1 to 250Ώ.
(b) Ask the supervisor to check the circuit.
(c) Close switch S.
(d) Vary R1 from 250 Ώ to 50 Ώ in steps of 50 Ώ.  For each setting of R1 record the reading I1 on the ammeter A1.
(e) Open switch S.
(f) Disconnect the unknown resistance, Rx from the circuit and connect   the O – 300mA ammeter, A2 as shown in fig. 2.







(g) Set R1 to 250Ώ.
(h) Close switch S
(i) Vary R1 from 250Ώ to 50Ώ in steps of 50Ώ.  For each setting of R1, record the reading I2 on the ammeter, A2.
(j) Calculate (I2-I1) and  (I1/(I1-I2) for each  Setting of R1        
(k) Tabulate your result as shown in Table 1.

 

      R1Ώ

 

   I1(A)

 

    I2(A)

 

 
  (I2-I1)(A)

yu     I1
yuu 



   I2-I1

      250

 

 

 

 

      200

 

 

 

 

      150

 

 

 

 

        50

 

 

 

 

(l) Plot a graph of R1(Ώ) the y-axis against  I1           on the x-axis
                                               we                                                                                            
                                                           I2-I1

(m)Determine the slope of the graph plotted in (l)

_____________________________________________________________________________________________________
Observation

The candidates were required to
(a) connect the circuit as shown and take current readings
(b) determine the slope m which must be within the range of Rx given.

The expected answers were

R1(Ώ)

I1(mA)

I2 (mA)

(I2-I1)(mA)

     I1
bb 



   I2-I1

250

30.0

  48.0

   18.0

1.6667

200

34.0

  60.0

   26.0

1.3077

150

40.0

  80.0

   40.0

1.0000

  50

60.0

240.0

 180.0

0.3333

   Note:    Rx is any value between 100Ώ and 200Ώ. 
   From the graph, slope m = y2-y1/x2-x1  Ώ      
                                                   

              =  150-0     =   150 Ώ
                  1-0
            Slope, m = 150Ώ

Candidates were able to connect and obtained readings from the experiment but some got inaccurate readings.

 

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