KCSE 2017 Electricity Paper 1 with Marking scheme

SECTION A (48 marks)

Answer all the questions in this section in the spaces provided.

1.  
   1. Name four methods of generating electricity used in Kenya.  (2 marks)
   2. Define each of the following levels of trade qualifications.   (2 marks)
      
      1. artisan
      2. technician
2.  
   1. Outline four major items that must constitute a Business Plan.   (2 marks)
   2. List four minimum steps followed to ensure electrical safety in an electrical workshop with respect to main supplies.    (2 marks)
3.  
   1. State two ways in which electric shock can be prevented in a laboratory.   (2 marks)
   2. A PN junction diode is connected to a 12 v dc supply through a series resistor of 500Ω The current flowing is 20 mA.
      
      1. Determine the p.d. across the PN junction diode  (2 marks)
      2. Determine the power dissipated in the junction.   (1 mark)
4.  
   1. Figure 1 shows an electric circuit. Find the current through R₂     (3 marks)
      
   2. Define the term 'e-waste'.    (1 mark)
5.  
   1. Name the logic gate shown in Figure 2.   (1 mark)
      
      Name
   2. Complete the truth table of the OR gate shown in Table 1.     (2 marks)
      Table 1
      

      INPUT 1	INPUT 2	OUTPUT
      0	0
      0	1
      1	0
      1	1

   3. Perform each of the following number conversions.     (4 marks)
      1. 101010₂ to decimal
      2. 23₁₀ to Binary
   4. Sketch the following circuit symbols
      1. Light Emitting Diode (LED)     
      2. Incandescent lamp     (2 marks)
6.  
   1. Name one application of each of the following electrical materials.     (1 mark)
      1. Copper
      2. Silicon
   2. An iron box sparks when connected to power and fails to function. Outline the procedure followed to trace the problem.    (2 marks)
7.  
   1. Using a schematic diagram, show how a lamp can be controlled from two different positions.    (2 marks)
   2. Determine the colour code of a carbon resistor whose value is 1500 ± 5%.    (2 marks)
8. Figure 3 shows a cross sectional construction of a moving iron instrument. Name the parts labelled A to F.   (3 marks)
   
9.  
   1. List four applications for inductors.   (2 marks)
   2. Define the term inductance as used in electric circuits.   (1 mark)
   3. A single phase step down transformer has a ratio of 8:1, a primary voltage of 3.3 kV and load of 6.6 kVA. Ignoring losses, calculate;   (6 marks)
      1. secondary voltage
      2. secondary current
10. Figure 4 shows a current carrying conductor.    (3 marks)
    1. Sketch the correct magnetic flux around the conductor.
    2. Indicate the direction of the current.
       

SECTION B (52 marks)

Answer any four questions from this section in the spaces provided.

Use the A3 paper provided:

11. Figure 5 shows an isometric drawing of a block.
    Draw FULL SIZE 1st angle projection the following views
    
    1. Front elevation in the direction of arrow F
    2. End elevation
    3. Plan    (13 marks)
       
12.  
    1. Define an a.c. generator.   (2 marks)
    2. Figure 6 shows the construction features of a simple a.c. generator.   (5 marks)
       
       Name the parts labelled A to F
    3. Figure 7 shows a moving coil instrument. Calculate the value of resistor R_m to enable it to read 0 - 100 V.
       (2 marks)
       
    4. Figure 8 shows a line diagram of equipment at the consumer intake point. Name the parts labelled A to F.
       (4 marks)
       
13.  
    1. Define the term magnet.   (2 marks)
    2. List three properties of a magnet.   (1½marks)
    3. Explain the theory of magnetism.   (3 marks)
    4. List three methods of demagnetisation.   (1½ marks)
    5. Draw and label a diagram of a core-type transformer.   (5 marks)
14.  
    1. Sketch and label a schematic diagram of a transistor in Common Emitter Configuration
    2. Given that ______________________ and _________________________
       Show that the Emitter current is the sum of collector and base currents.    (6 marks)
15.  
    1. Figure 9 shows an RLC circuit. Determine the total impedance.    (7 marks)
       
    2. Figure 10 shows a metal work piece.
       1. List the tools used to fabricate the piece.
       2. For each tool listed in (i) state one function.   (6 marks)
          

MARKING SCHEME

1.  
   1.  
      • Geothermal
      • Solar
      • Biomass
      • Wind power
      • Hydropower 
      • Fuel
        Any (4) x ½ = (2)
   2.  
      1. Artisan - a skilled worker who practices a trade or handcraft(1)
      2. Technician - a specialist in the technical details of a subject or occupation. (1)
2.  
   1.  
      • Executive summary
      • Company description
      • Market Analysis
      • Organization and Management 
      • Service or product line
      • Marketing and sales
      • Funding request 
      • Financial projections
        Any (4x½)= (2)
   2.  
      • Install new electrical system (standardization).
      • Maintain all electrical installation in and working order. 
      • Provide enough socket outlets for equipment in use. 
      • Avoid overloading socket outlets.
      • Provide any accessible and clearly identified switch ratings.
      • For portable equipment connect to nearby socket outlets.
        Any (4 x ½)=(2)
3.  
   1.  
      • Never mix water and electricity.
      • Pay attention to what appliances are telling you. 
      • Install ground fault circuit tests.
      • Make sure you are using the right size circuit breakers and fuses.
      • Protect kids with outlet covers.
      • Avoid cube taps and other outlet stretching devices.
        Any (2 x 1)=(2)
   2.  
      1. P.d. across = 500 x 0.02
                         = 10V.   (1)
         P.d. across the junction is therefore
         (12−10) = 2V.  (1)
      2. Power dissipated in the junction
         P=VI
           =0.02 x 2
           = 0.04 W or(1)
            =40mW
4.  
   1. Current entering = current leaving
      Assuming 120Ω branch = V
      150=(v− ¹²/₂₇₀ + ^V/₁₂₀ ) (1)
      0.15 − 13V − ⁴⁸/₁₀₈₀
      162 = 13V − 48
      210 = 13V(1)
      (210) = V
       (13)
      Current in 120Ω branch = ^V/₁₂₀
      ⇒   210     = 134mA    (1)
         13×120
   2. e-waste is be defined as discarded computers, office electronic equipment entertainment devices, mobile phones, television sets, refrigerators. It includes used electronic destined for re-use, resale, salvage, recycling or disposal. AND gate (1)
5.  
   1. AND gate (1)
   2.   
      

      INPUT 1	INPUT 2	OUTPUT
      0	0	0
      0	1	0
      1	0	0
      1	1	1

   3.  
      1. 101010 into decimal 
         2⁵2⁴2³2²2¹2⁰
         101010 (1)
         = 32 + 0 = 8 + 0 +2 +0
         = 42 ten (1)
      2. 23 into binary
          (1)
         =10111 two (1)
   4.  
      1.  
         
      2.  
         
6.  
   1.  
      1. Copper-electrical conductors
      2. Silicon-In semiconductor devices
         (Any 2x½)=1
   2.  
      • Check fuse on the top plug.
      • Check continuity of the supply cord.
      • Check continuity of the coil in the iron box.
        Any 2 x 1 =
7.  
   1.  
      (½x4)=2
   2. Brown  Grey  Red  Gold
      @4 x ½ = 2
8.  
   • A-Pointer
   • B - Air damping chamber
   • C - Spring
   • D- Balance weight
   • E-Coil
   • F - Moving iron
     6x½=3 
9.  
   1. Used in:
      • Filters
      • Sensors
      • Transformers
      • Motors
      • Energy storage
        Any (4 x ½ ) = (2)
   2. Inductance is the property of an electric conductor or circuit that causes an electromotive force to be generated (1) by a change in the current flowing.
   3.  
      1. V_P X I_P = V_s x I_s
         As the ratio is 8:1, step down.
         See voltage V_s = V_p
                                   8
                              = 3300 = 4125 } - (1)
                                     8
      2. Assuming no losses input = output  (1)
         V_P X I_P = V_s x I_s
         ⇒ I_s = V_pI_p = (6.6 x 1000) (1)
                      V_s           412.5
         =16A (1)
10.  
             
    1. Correct
       • Magnetic flux
       • Current entering board (2 x ½)1
       • Current leaving board (2 x  ½)1
    2. Correct current direction
11.  
    
    Faces, Front Elevation (2 x 1) - 2
    Faces End elevation (3 x 1) - 3
           hidden details
    Plan face (1 x 1) - 1
    hidden detalls (5 x 1) - 5
    Correct placement -1
    TOTAL 13
12.  
    1. An alternator is an electrical machine which converts mechanical (1) energy into alternating electrical energy (1).
    2.  
       • A-magnet
       • B-magnetic field
       • C-Coil (armature)
       • D-Slip rings
       • E-Shift
       • F-Brushes
         Any 5X1=5
    3. At F.S.D. I = 0.030A
                    V = 0.090V
       V_r(across terminals) = 100V
       ⇒ Rm=resistance of multiplier
       Voltage (across resistor) = (100 − 0.090V)
                                           = 99.91V.  (1)
       Since R = ^V/₁
       ⇒R_m = 99.91 (½)
          R_m= 3330.33Ω (½)
    4.  
       • A-Final circuit
       • B-Consumer unit
       • C-Main switch
       • D-Energy meter
       • E-Cut out
         F-Supply cable
         (6 x ½ ) = 3
13.  
    1. A magnet is any material that affects iron or material containing iron. (1)
    2. Properties of a magnet
       • All have 2 poles N and S. 
       • Exert forces on each other.
       • Surrounded by a magnetic field.
         3 x ½ =1½
    3. Theory of magnetism 
       • Whethera material is magnetic or not. 
       • In some materials groups of atoms are in tiny areas called domains. 
       • Arrangement of domains determine state.
       • When domains move, the magnet is demagnetized or loses is magnetic properties. (3)
    4.  
       • Dropping or hitting it hard
       • Putting it in a strong magnetic field opposite its own
       • Increasing the temperature.
    5.  
       
       Drawing (5x½)=2½
       Labelling (5x½)=2½
14.  
     
    1. 
       
       Correct components (6x½)=3
       Labelling of components (6x½)=3
       Correct configuration  =1
    2.  
       
15.  
    1.  
       
    2. Tool use
       • Steel rule - measuring and making
       • Scriber - marking
       • Engineers square - marking and checking for squareness
       • Centre punch - locating holes
       • Hacksaw - cutting metals
       • Twist chill - drilling
       • Files - deburring
         any other suitable answer ( 6x½)x2 =6