waecE-LEARNING
Applied Electricity 1 , May/June 2011  
Questions:   1 2   Main
General Comments
Weakness/Remedies
Strength


Question 1

AIM: To show the relationship between current and voltage in series-connected loads

  1.  Connect the circuit as shown in Figure 1.
  2.  Ask your supervisor to check the circuit connection.
  3.  Copy Table 1 into your answer booklet.

Variac voltage(V)

   Condition of bulbs

     A(A)

    V1(V)

    V2 (V)

   40 W

    60 W

     100

 

 

 

 

 

     120

 

 

 

 

 

     140

 

 

 

 

 

     160

 

 

 

 

 

     180

 

 

 

 

 

     200

 

 

 

 

 

  1.  Close switch S.
  2.  Set the variac to 100 V.
  3.  Read and record in Table 1 the meter readings A, V1 and V2.
  4.  Repeat steps (e) and (f) for voltages 120 V to 200 V as shown in Table 1.
  5.  Observe and state the conditions of the bulb as the voltage is varied from      100 V to 200 V.
  6.  Compare the results of V1 and V2.
  1.  State your observations on whether there are differences or similarities in  the values of V1 and V2.
  2. Calculate R of the 60 W bulb when the variac voltage is 200 V.


Observation

The candidates were expected to connect the circuit as shown in Fig.1, measure and record in Table 1 the ammeter readings, voltmeter readings and make some observations and calculate some values.

The expected answers were:

Variac voltage(V)

   Condition of Bulbs

     A(A)

    V1(V)

    V2 (V)

   40 W

    60 W

     100

     ON

     OFF

    0.042

   60.48

   40.32

     120

     ON

     OFF

    0.050

   72.00

   48.00

     140

     ON

     OFF

    0.058

   83.52

   55.68

     160

     ON

     DIM

    0.067

   96.48

   64.32

     180

     ON

     DIM

    0.075

 108.00

   72.00

     200

     ON

     DIM

    0.083

 119.52

   79.68

  1. The results of V1 (V) and V2 (V) are not equal.
  2. The difference in values of V1 (V) and V2 (V) is due to the difference in the voltage of the bulbs

                                  OR
The 40 W bulb possesses lower resistance while the 60 W possess higher resistance to current leading to different voltage drop.

  1.  P = IV = I2R

 R60W =  =  = 960

The candidates, as reported, understood the question and carried out the actions required. But they failed to obtain accurate readings from the instruments which marred their performances. The observations and calculations they were required to make were all based on the readings. The moment the readings are not accurate, all other actions on it are also inaccurate. 

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