Kenya Certificate Of Secondary Education(KCSE 2013) Electricity Paper 2

EXERCISE 1

1. Using materials, components and equipment provided, perform the following tasks.
   
   1. Connect the circuit shown in figure 1. (3 marks)
      Let the examiner check your work.
      
   2. Close switch S.
   3. Adjust the potentiometer for the ammeter to obtain current values in table 1 and in each case record the corresponding voltage values
      Table 1
      

      Current I(mA)	40	100	200	240	260
      Voltage (V)
      V   I

   4. Calculate the values of   V and record them in the spaces provided in the table.
   5. Use the values in the table to draw a graph of voltage against current.
   6. Determine the slope of the graph. (2 marks)
   7. From the graph, determine the voltage, V when the current I = 160 mA.
      V = ..................................................................................................(1 mark)
   8. State the purpose of the experiment. (1 mark)
      
      EXERCISE 2
2. Use the tools, equipment and materials provided to make the bracket shown in figure 2. (20 marks)
   
   EXERCISE 3
3. Figure 3 shows a block diagram of the electronic circuit provided.
   
   Perform the following tasks:
   1. With the switch S open, connect the circuit to the DC power source. Let the examiner check your work. (1 mark)
   2. Set the potentiometer to 0 Ω as measured with ohmeter. Select a value of resistor shown in table 2 and in each case, do the following:
   3. close the switch, measure the voltage and record in table 2. (5 marks)
      Table 2
      

      Resistor (Ω)	VR	P = VR R
      56
      220
      390
      680
      1000

   4. Calculate the power dissipated by each resistor and complete table 2. (5 marks)
   5. From the graph, determine the value of R for which there is maximum power transfer. (1 mark)
      
      EXERCISE 4
4. Use the components and equipment to connect the circuit illustrated in figure 4. Let the examiner see your work
   
   Perform the following tasks:
   1. Switch on the power supply.
   2. Adjust the power supply to obtain each of the voltage values across U as shown in table 3 and in each case, record the corresponding current: (5 marks)
      Table 3
      

      V	0.4	0.5	0.6	0.7	0.8
      I

   3. Switch off the power supply and reverse its connections.
   4. Adjust the power supply to obtain each of the voltage values across U as shown in table 4 and in each case, record the corresponding current. (5 marks)
      Table 4
      

      V	-0.5	-1	-3	-4	-5
      I

   5. Use the values of I and V from tables 3 and 4 to draw the graph of current (I) against voltage (V) on the same axes. (7 marks)
   6. From the shape of the graph, identify component U. 
      
      EXERCISE 5
5. Figure 5 shows the layout of a lighting installation. Using PVC sheathed cables, install the circuit such that the lamps are controlled at one point. (20 marks)