Electricity Paper 2 Questions and Answers - KCSE 2022 Past Papers

QUESTIONS

EXERCISE 1

1. Figure 1 shows an electronic circuit.
   
   
   1. Using the board and items provided, connect the circuit as shown.
      Let the examiner check your work. (5 marks)
   2. Adjust the power supply in chain the vahu shown in Table 1, and for ich voltage value, measure and record the corresponding value of voltage (V) and current (mA). (10 marks)
      Table 1
      

      SUPPLY VOLTAGE, ES(V)	VOLTAGE (V)	CURRENT (mA)
      1.5
      3.0
      4.5
      6.0
      7.5
      9.0

   3. Using the values in Table 1, plot a graph of current (mA) against voltage (V). (4 marks)
   4. From the graph, obtain the zener potential voltage.   (1 mark)
      V_z=.............volts (1 mark)

EXERCISE 2

2. Figure 2 shows the development and pictorial view of a casing of a switchgear.
   
   Using the tools, equipment and materials provided:
   1. fabricate the casing
   2. solder the flaps
      (20 marks)

EXERCISE 3

3. Figure 3 shows an electric circuit.
   
   
   1. Connect the circuit as shown in the Figure (6 marks)
      Let the examiner check your work.
   2.  
      1.  The power supply is pre-set to 10 V DC.
         Very the potentiometer to obtain each of the voltages shown in Table 2. (3 marks)
      2. For each values in Table 2, calculate and record the power dissipated in the potentiometer
         (3 marks)
         Table 2
         

         Voltage (v)	0	2	4	6	8	10
         Current (mA)
         Power diddipated

   3. Plot a graph of power against current.
   4. From the graph:
      1. state the maximum power dissipated by the potentiometer
         Maximum power dissipated  (1 mark)
      2. determine the resistance of the potentiometer at maximum power
         Resistance (1 mark)

EXERCISE 4

4. Figure 4 shows a block diagram of a prefabricated circuit provided.
   
   
   1. With the switch open, perform each of the following tasks:
      1. Connect the power supply set at 9V DC across points labelled P and Q (1 mark)
      2. Connect the ammeter across terminals marked A and B (1 mark)
   2. Close the switch, vary the potentiometer from minimum to maximum.
      1. State your observation (4 marks)
      2. Measure the values of current at
         1. minimum...........mA  (1 mark)
         2. maximum..........mA  (1 mark)
   3. Explain the reason for your observation in 4(b).
   4. Draw a schematic diagram of the circuit.

EXERCISE 5

5. Figure 5 shows the layout of a power final circuit
   the consumer control unit is pre-installed.
   
   Using PVC sheathed cables, install the circuit
   (20 marks)

MARKING SCHEME

1.  
   2. Table 1
      10 measurements
      10x1 =10 marks
   3.  
      
      Drawing graph
      Axes 2x 1⁄2=1
      Plotting.-1
      Joining curves 1
      Neatness 1
                 =4
   4. Obtaining the liner potential = 1 mark
2.    (20 marks)
3.  
   1.  (6 marks)
   2. Table 2
      Current values   3 marks
      Power dissipated  3 marks
   3. Graph
      Axes 2x1=2
      Plotting = 1
      Joining curves=2
      Neatness =1
   4.  
      1. Maximum power dissipated 1 mark
      2. Determining the resistor of potentiometer 1 mark
         P = PVI or V²
                     R
         P I²R_L
4.  
   1.  
   2.  
      1. Stating observation
         Led dimness and brightness
      2. Measurement of current values
   3. Explanation of remon for values in (b) .
   4. Drawing the circuit
      
      
5. To be marked fully at examination centre