KCSE 2018 Electricity Paper 2 with Marking Scheme

QUESTIONS

EXERCISE 1

1. Using the materials, equipment and measuring instruments provided, perform the following tasks:
   1. Connect the circuit as shown in Figure 1.  (3 marks)
      Let the examiner check your work.
      
      Figure 1
   2. Turn the power ON and adjust the potentiometer to obtain each of the voltages (VR). Shown in Table 1. In each case read and record the corresponding current I. (6 marks)
      Table 1
      

      VR	I(mA)	POWER(mW)
      3
      4
      5
      6
      7
      8

   3. For each value of VR, calculate the power dissipated in the 4700 resistor and complete the table.(6 marks)
   4. Using the values in Table 1, draw the graph of power against voltage VK. (4 marks)
   5. State two applications of the circuit.(1 mark)

EXERCISE 2
2. Use the tools, equipment and materials provided to make an electronic circuit casing shown in Figure 2. (20 marks)
Let the examiner check your work.

Figure 2

EXERCISE 3

1. Using the components and equipment provided, connect the circuit as shown in Figure 3.
   Let the examiner check your work.(6 marks)
   
   Figure 3
2. Put ON the power supply. Close switch S, measure and record current through the following resistors:(3 marks)
   R₁ = .............................................
   R₂ = .............................................
   R₃ = .............................................
3. Measure the total circuit current, I_T. (2 marks)
   I_T  = .............................................
4. Measure and record the voltages across the following resistors: (6 marks)
   R₁ = .............................................
   R₂ = .............................................
   R₃ = .............................................
5. Using the values in (c) and (d) above, calculate the value of the resistors: (3 marks)
   R₁ = .............................................
   R₂ = .............................................
   R₃ = .............................................
   R_T = .............................................

EXERCISE 4
4. Figure 4 shows a block diagram of a prefabricated electronic circuit.

Figure 4
Using the equipment and accessories provided, perform the following tasks: 

1. Connect the circuit to the power supply through the PBNO switch provided.
   Let the examiner check your work.(2 marks)
2. Press and hold the PBNO switch for about 10 seconds and describe the behaviour of the LEDS:(1 mark)
3.                              
   1. Connect the 10kΩ resistor at A and B.
      Let the examiner check your work.(1 mark)
   2. Press and hold the switch. Count the number of times each LED flashes in one minute:
      RED.............................................
      GREEN.............................................(4 marks)
4. Draw the schematic diagram of the circuit.(10 marks)
5. State:
   1. the name of the circuit(1 mark)
   2. application of the circuit.(1 mark)

EXERCISE 5
5. Figure 5 shows a layout of a final circuit, using PVC conduit wiring system, install the circuit such that the lamp is controlled by the one way switch.(20 marks)
Let the examiner check your work.

Figure 5

MARKING SCHEME

EXERCISE 1

EXERCISE 3

EXERCISE 4