Electricity Paper 2 Questions and Answers - KCSE 2021 Past Papers

EXCERCISE 1

1. Figure 1 shows an electrical circuit.
   
   
   1. Using the components, materials and equipment provided, connect the circuit as shown in Figure 1 on a breadboard.
      Let the examiner check your work. (6 marks)
   2. With S₁ ON, measure and record the total current I_T
      I_T = ..............mA        (1 mark)
   3. Measure and record the currents. (3 marks)
      I₁ =.......................(mA).
      I₂ = .....................(mA).
      I₃ = ......................(mA).
   4.  
      1. In the circuit, replace R₃ with R₄
         Let the examiner check your work.      (2 marks)
      2. Repeat steps (a) to (c).    (4 marks)
         I_T = ...................(mA)
         I₁ = ...................(mA)
         I₂ = ....................(mA)
         I₃ = .....................(mA)
   5.  
      1. Explain the relationship between currents I₂ and I₃ (2 marks)
      2. State the effect on the current 1_T when R₃ is replaced with R₄  (2 marks)

EXERCISE 2

2. Using the tools, materials and equipment provided, fabricate the bracket shown in Figure 2.   (20 marks)
   

EXERCISE 3               

3. Using the tools, materials and equipment provided,carry out the following tasks:
   
   1. Terminate the three core heat resistant flexible cable to the top plug and the iron box. (15 marks)
   2. Turn the thermostat switch 'ON' at maximum position. (1 mark)
   3. Measure and record the values of Resistance of the element in Table 1.  (4 marks)
                                                             Table 1
      

      TEST BETWEEN	READING OBTAINED
      1) Live and Neutral at Plug
      2) Live and Earth at Plug
      3) Earth at Plug and Iron box body
      4) Neutral at Plug and Iron box

EXERCISE 4

4. Figure 3 shows the block diagram of the electronic circuit marked R.
   
   Use the equipment and accessories provided to perform the following tasks:
   
   1. Set the power supply voltage to 10 V output.
   2. With the power supply off and switch S off connect the equipment to the terminals of circuit R at points + and Θ as shown.
      
      1. A and B a voltmeter
      2. X and Y an ammeter
      3. S and T a power supply
         Let the examiner check your work.                   (3 marks)
   3. Turn the power supply ON and turn the switch ON.
      Adjust the potentiometer to obtain the R_t values as shown in Table 2.
   4. In each case, measure and record in table 2 the corresponding values of circuit current I and calculated values of circuit power in watts.
                                              Table 2
      

      RL(Ω)	I(A)	P(W)
      0
      5
      10
      15
      20
      25
      30
      40
      60
      80
      100

                                                                                                                 (11 marks)
   5. Plot a graph of power against load resistance on the graph on the last page. (4 marks)
   6. Determine the value of load resistance that allows maximum power transfer from the plotted graph in 4(d).  (2 marks)

EXCERCISE 5

5. Figure 4 shows the layout of a lighting final circuit.
   
   Using PVC sheathed cable, install the circuit such that the lamp is controlled from one point.  (20 marks)

MARKING SCHEME

                                                                  EXERCISE 1

1 (a)	6 marks at institution (exam centre)	6 marks
(b)	1 mark (exam centre)	1 mark
(c)	Sample data-3 marks from examiner	3 marks
(d)	Sample data - 6 marks	6 marks
(e)	Relationship between currents I2 and I3 R2 and R3 are series circuits and currents I2 and I3 are same i.e. I2 = I3 Effect of current IT If R3 is greater than R4 the less current flows. If R4 is greater than R3 then more current flows in the circuit.                                                                                       Total 20 marks	2 marks     2 marks
2	Everything to be marked at the exams centre	20 marks
EXCERISE 3
(a)	- 15 marks  Marked at the institution (exam centre)	15 marks
(b)	Turning switch ON (exam centre)	1 mark
(c)	Sample data for measurements depends on the resistor of element and type of iron box. Sample data from the examiner.	4 marks
4 (c)	Values   (sample data results from examiner)	11 marks                  2    2  1
(d)	Labelling axes   Plotting points  Joining curve smoothly
(e)	Value of load resistance for maximum power is 25Ω      (Sample data results from examiner)           Sub-total   17 marks	1
5	Everything marked at the exam centre.	20 marks