ELECTRICITY PAPER 1 - 2019 LAINAKU JOINT MOCK EVALUATION EXAMINATION

SECTION A (48 marks)
Attempt all questions in this section in the spaces provided

1. 1. State the most immediate action to be taken when rescuing a worker found unconscious and still in contact with a live wire           (1 mark)
   2. List two safety precautions taken while drilling through a piece of sheet metals (2 marks)
   3. State the role of Directorate of Industrial Training                    (1 mark)
   4. Outline four major items that must constitute a business plan (2 marks)
2. 1. The range of a moving iron instrument of resistance 8 ohms is extended by using   a shunt resistor of 0.04 ohm. If the full scale deflection current is 10mA, determine the maximum current that the modified instrument can measure  (2 marks)        
   2. State two advantages and two disadvantages of the moving iron instrument over moving coil instrument         (2 marks)
3. 1. List two power company equipment and two consumer’s equipment found at a domestic consumer’s intake point.     (2 marks)
   2. State one advantage and one disadvantage of fluorescent lamps over filament lamps             (2 marks)
4. State two reasons why the rotating field alternator is preferred to the rotating armature type      (2 marks)
5. 1. After installing new cells in a 2 cell torch it failed to light when switched on. State two possible causes for the failure                                                 (2 marks)
   2. Three capacitors are connected as shown in Figure 1
      
      Calculate:
      1. The equivalent capacitance
      2. Charge stored in the 26µF capacitor                         (4 marks
6. Sketch and label the schematic diagram of a dc shunt motor connected to a supply                                                                                                             (4 marks)
7. 1. Name the materials used to make the following parts of ac machine in Table 1       and in each case state one reason why the material is used                   (3 marks)
      Table 1
      

      Part	Material	Reason
      Brushes
      Slip rings

      State three factors to consider when choosing motor for a particular installation                                                                                                             (3 marks)
8. 1. List four layout tools used in metal fabrication                                  (2 marks)
   2. Describe three characteristics of magnetic lines of force             (3 marks)
9. 1. Name two types of inductor cores                                                      (1 mark)
   2. State two factors that determine inductance of a coil             (2 marks)
10. 1. Determine the resistance of each of the following carbon resistors if their colour     code is:
       1. Blue Orange Brown Silver
       2. Grey Red Yellow                         (2 marks)
    2. Figure 2 shows a resistor network
       
       Find value of current I                                                (2 marks)
    3. Name the logic gate shown in figure 3 below
       
       Figure 3
       Name ………………
    4. Complete the truth table of the AND gate shown in Table 2 (2 marks)
       

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

SECTION B  (52 marks)Table 2
Answer any four questions from this section in the spaces provided

11. Figure 4 below shows a block drawn in isometric projection
    
    Figure 4
    Using first angle orthographic projection, draw the following views full size
    1. Front elevation in the direction of arrow F
    2. End elevation in the direction of arrow E
    3. Plan                                                                                                 (13 marks)
12. 1. State three advantages of toroidal type transformer over shell type transformer                                                                                                                               (3 marks)
    2. 1. Outline three assumptions made in order to consider a transformer as an                             ideal machine                                                                          (3 marks)
       2. A5000/500V, 10KVA ideal single phase transformer has 40 turns on the                            Calculate:
          1. primary turns
          2. primary full load current
          3. secondary full load current             (7 marks)
13. 1. State the phase relationship between current and voltage in circuits that are            purely:
       1. Resistive
       2. Inductive                                                             (2 marks)
    2. Figure 5 shows an RLC circuit
       
       Figure 5
       Calculate the:
       1. Inductive reactance
       2. Capacitive reactance
       3. Circuit impedance
       4. Circuit current
       5. Power dissipated in the circuit             (11 marks)
14. 1. List three metal parts that are exempted from earthing in a domestic installation                 (3 marks)
    2. Give three reasons why a verification of polarity test is carried out in a completed domestic installation           (3 marks)
    3. Draw a line diagram of a national grid system showing typical voltages at each stage                (7 marks)
15. 1. Draw a labelled circuit diagram of a PNP transistor amplifier in common base   configurations              (3 marks)
    2. Table 3 below shows a bill of materials used to construct a stabilized dc supply
       

       No	Description of material	Quantity
       1	Double pole switch	1
       2	Double wound transformer	1
       3	Rectifier diodes	4
       4	Electrolytic capacitor	1
       5	Carbon resistors	1
       6	Zener diode	1
       7	Connecting wires	Several

       Draw a circuit diagram of the power supply                                                  (10 marks)

MARKING SCHEME

1. 1. switch off power supply
   2. put on gloves
      don’t adjust drill when in use
      make sure all connections are safe
      don’t wipe shavings by hand. Use brush
      never leave it unattended
      ensure cables don’t obstruct other workshop users
      switch off and unplug when not in use
   3. establish national training standards and common working conditions for craft and technician apprentices
      promote and develop systematic craft and technician apprenticeship programmes in industries
      meet the needs for skilled workers in industry
      create opportunities for school leavers to undertake training in industry
   4. executive summary
      description of business
      description of product/ service
      market analysis
      competitive analysis
      operations management
      financial components
2. 1. Rm=8Ω, Rs=0.04Ω, Ifsd=10mA, Is=?
      IfsdRm=IsRs
      Is=IfsdRm/Rs
      Is=(10mAx8Ω)/0.04Ω
      Is=2000mA
      Im=2000+10
      Im=2010mA

   2. 	Moving coil	Moving Iron
      Advantages	·         Uniform scale ·         Consume less power ·         Damping is simple and effective	·         Can measure ac and dc currents ·         Cheaper than moving coil ·         Are robust and simple in construction ·         Torque/ weight ratio is high, hence less friction error
      Dis-Advantages	·         Can measure only dc current ·         Magnets weaken with time	·         Scale not uniform ·         Low input impedance ·         Consume more power than moving coil

3. 1. power company Equipment-Neutral link, service fuse, KWH metera)
      Consumer Property-Main switch, Main fuse, Distribution board
   2. Advantage-Long lasting, more efficient, produce less heat
      dis-advantage- Expensive
4. Light and can run at high speeds
   Can generate high voltages due to high speed
   Rotor is simple and robust in construction
   Current ratings are high
   It’s easier to insulate armature coils for high voltages generated
5. 1. Cells facing wrong direction, Bulb damaged, Switch damaged
   2. 1. Ct=26µF+(40µFx60µF)/(40µF+60µF) Ct=50µF
      2. Q=26µFx12V
         Q=312µ
6. 
   

7. Part	Material	Reason
   Brushes	carbon	lubricant
   Slip rings	copper	Good conductor of electricity

1. Power required, no of phases i.e. single or 3 phase, type of load i.e. whether constant       speed or high starting torqueb) -frequency of starting and stopping

8. 1. scribers, steel rule, divider, square, center punch
   2. pass through all materials, move from north to south outside magnet, those moving same direction repel, form complete loops
9. 1. Ferrite core, iron core
   2. Length, number of turns, cross section area
10. 1. 1. 630Ω±10%     
       2. 820KΩ±20%
    2. I=10V/ (30+10) Ω, I=0.25A
    3. OR

    4. INPUT 1	INPUT 2	OUTPUT
       0	0	0
       0	1	0
       1	0	0
       1	1	1

11. 
12. 1. Better magnetic linkage, cheaper, small in size per kilovolt –ampere rating
    2. 1. no copper loss (0 resistance), no iron loss, all magnetic field in primary links to                               secondary, negligible emf required to set up the flux
       2. 1. Np=(5000Vx40t)/500V Np=400 turns
          2. Ip=10000VA/5000V, Ip=2A
          3.  Is=10000VA/500V, Is=20A
13. 1. 1. Current and voltage are in phase     
       2. Voltage leads current by 90^o
    2. 1. Xl=2πfl,          Xl=2πx50Hzx0.4H, Xl=125.664Ω
       2. Xc=1/(2πfC)=1/(2πx50x50x10^-6), Xc=127.324Ω
       3. Z=√(R^2+〖(XL-XC)〗^2 ,Z=50.028Ω
       4. I=E/Z, I=240V/50.028,          I=4.8A
       5. P=I²R, P=4.8²x50Ω    P=1152W
14. 1. metal clips, catenary wire, metal chains for suspension of lighting fittings, metal    caps of lamps, screw or metal name plate
    2. -make sure single pole switches, circuit breakers, fuses etc. are connected on live conductors only
       ensure outer contacts of bayonet and Edison screw lamp-holder are connected to neutral conductor
    3. 
15. 
    1.