KCSE 2019 Electricity Paper 1 Questions with Marking Scheme

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KCSE 2019 Power Mechanics Paper 2 Questions with Marking Scheme

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KCSE 2019 Electricity Paper 2 Questions with Marking Scheme

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Electricity Paper 1 (448/1)

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

1. Name four equipment belonging to the supply authorities at consumer's intake point. (2 marks)
2. List four types of capacitors.(2 marks)
1. Draw the circuit diagrams for each of the following d.c. generators:
  1. Separately excited generator
  2. Compound wound generator(4 marks)
1. Name two types of semi-conductor diodes and state one application in each case.(2 marks)
2. Draw an NPN transistor in common base configuration.(3 marks)
1. Name three types of measuring instruments and for each type state their use. (3 marks)
2. Sketch each of the following hand tools:(4 marks)
  1. flat screw driver
  2. ball pein hammer
Make a free hand oblique drawing of a conduit switch box.(3 marks)
1. List four categories of institutions which offer artisan certificate courses in electrical trade.(2 marks)
2. Outline the procedures of using a fire extinguisher(2 marks)
1. State three precautions to be observed to avoid accidents from clectrical overhead power lines.(3 marks)
2. Explain two ways of identifying faults in electronic circuits during trouble shooting.(2 marks)
1. State four factors that determine the inductance of a coil.(2 marks)
2. Two capacitors have capacitances of 6uF and 4uF respectively. Determine the total capacitance when they are connected in:
  1. Parallel
  2. Series (4 marks)
1. State two factors that determine the strength of an electromagnet.(2 marks)
2. 1. Draw the sketches of magnetic field around two parallel conductors carrying current in the opposite directions.(2 marks)
  2. State what happens between the two conductors in b(i) above.(1 mark)
1. State two types of electricity tariffs.(1 mark)
2. The average daily power consumption of a domestic consumer is as follows:
  
  Lighting 1.0 kw for 5 hours
  Instant shower 3.0kw for 2 hours
  Cooking 6.0 kw for 3 hours
  Electric heater 4.0 kw for 2 hours
  Determine the:
  1. daily consumption in kWh
  2. cost of energy in Ksh if the rate is 70ct per unit(4 marks)

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

1. Define each of the following terms as used in alternating currents:
  1. Cycle
  2. Frequency
    (2 marks)
2. A sinusoidal voltage trace displayed on an oscilloscope has peak to peak voltage of 12 V and a period of 20 ms.
  Sketch and label the waveform.(3 marks)
3. A coil of inductance 9.55 mH and resistance 42 is connected across a 200 V 50 Hz supply
  Calculate the
  1. Inductive reactance
  2. Impedance
  3. Supply current
  4. Phase angle
    (8 marks)
1. List two accessories used in PVC conduit installation and in each case state their function. (2 marks)
2. State two possible causes for a fluorescent lamp not to start. (2 marks)
3. 1. Outline four IEE regulations requirements regarding 13A socket outlets.(4 marks)
  2. Draw a wiring diagram of a lighting circuit comprising of two lamps L, and L controlled by one way switches S, and S, separately through a joint box. (5 marks)
1. Describe the construction of the following parts of a D.C. machine:
  1. Yoke
  2. Poles
    (4 marks)
2. A 100K VA, 11 KV/240 V single phase transformer has 800 turns on the primary side.
  Calculate the:
  1. Primary current
  2. Number of secondary turns (6 marks)
3. State three IEE regulations regarding bell transformers. (3 marks)
1. Sketch the symbols for each of the following logic gates:
  1. NAND
  2. NOR
  3. OR
    (3 marks)
2. Figure 1 shows a transistor circuit. Take β= 100 and neglect V_nr
  Find the value of V_ce(6 marks)
3. Figure 2 shows an amplifier circuit whose gain is 100. Neglecting V
  Find the value of
  1. I_B
  2. I_C
  3. V_ce
Figure 3 shows three views of a solid drawn in 1 angle projection. Draw full size an isometric vicw of the object making comer X the lowest point. (13 marks)

MARKING SCHEME

1. Equipment belonging to supply authority
  - Energy meter
  - Cut out
  - Supply cable
  - Sealing chamber
    4 x ½ = (2 marks)
2. Conducting materials
  - Paper capacitors
  - Electrolytic capacitors
  - Mica
  - Tantulum
  - Air capacitor
  - Ceramic capacitors
    Any 4 x ½ = (2 marks)
1. 1. Separately excited
    Separately exited
    
    Correct circuit = 2 marks
    Labelling 2 x ½ = 1 mark
    3 marks
    (1½ marks)
  2. Compound wound generator
    Compound
    
    (1 ½ marks)
1. Types of diodes
  1. LED (1) - used in displays
  2. Zener diode (1) - used as voltage regulator (1)
  3. PN junction diode - used in rectification.
    Any 2x1 = (2 marks)
2. Common base amplifier for n-pn transistor
  
  Circuit - 3 x ½ = 1½
  Labelling 3 x ½=1½
  3 marks
1. Measuring instruments
  - Voltmeter (½); measuring voltage (½).
  - Ammeter (½); mcasuring current (½)
  - Ohmeter (½); measuring resistance (½)
  - Wattmeter(½); measures power (½)
    Any 6 x ½=(3 marks)
2. 1. (2 marks)
  2. Correct sketching 2 x 1=2 marks Proportionality 2 x 1 = 2 marks
1. Correct sketch - 1
  Oblique - 1
  Proportionality - 1
  3
  (3 marks)
1. Institutions that offer artisan course.
  - Youth polytechnics
  - National youth service
  - Technical institutions
  - Institutions of technology
  - Technical training institutes
    4 x ½ = (2 marks)
2. Procedure for using a fire extinguisher,
  - Hold the extinguisher upright then remove safety pin or cap.
  - Direct the nozzle to base of flame.
  - Press the level or strike the knob.
  - Spray the base of the fire.
    4 x ½ =2 (2 marks)
1. Precautions to prevent accidents from overhead powerlines.
  - Never attempt to climb electric power posts.
  - Do not touch broken overhead cables.
  - Avoid climbing trees near power lines.
  - Avoid falling trees near powerline.
  - Accept other suitable responses.
    3 x1= (3 marks)
2. Identifying faults
  - Physical inspection by looking at the circuit components to determine shape and colour changes.
  - Circuit analysis by taking measurements comparing what is in the service manual.
  - History of the problem.(1 mark)
2. In parallel
  C=C₁+C₂=6μF +4μF= 10μF
  (2 marks)
  In series
  C = C₁ C₂ = 6 x 4 = 24 = 2.4μF
  C₁ + C₂ 6 + 4 10
  (2 marks)
1. - Number of turns in the coil.
  - Amount of current that flow through coil.
  - The type of core material.
  - The length of coil.
    Any 2 x 1=(2 marks)
2. 1. Field produced by two parallel conductors(2 marks)
    
    Flux lines around the two conductors carrying current in the opposite direction repel each other.
    Explanation - 1 mark
1. Types of tariffs -
  - Two part tariff
  - Plot rate tariff
    Accept any other tariff
    Any 2 x ½= (1 mark)
2. 1. W=Pt
    =(1.0x 5) + (3x2)+(6x3)+(4x2)
    = 5+6 +18+8
    = 37kwh
  2. Cost of energy in ksh
    = 37 x 70= 25.9 ksh
1. - Cycle - one complete series of variations in a waveform.
  - Frequency- the number of cycles completed in one second.
2. - (3 marks)
3. - R=4π
    L = mH=9.55×10^-3H
    f=50Hz
    V=200 V
    1. Inductive reactance
      X1 = 2πfL (1 mark)
      =2π(50)(9.55x10^-3)
      =3:H
    2. Impedance
      Z = √R²+XL²
      =√4² +3²= 5H
    3. Supply current
      I= ^V/_Z = ²⁰⁰/₅ = 40A
    4. Phase angle between
      tanθ = ^XL/_R
      θ = tan^-1 ^XL/_R
      tan^-1³/₄
      = 36.87º Lagging
      (1 mark)
1. - Coupler - Used to connect two conduits together.
  - Circular boxes enable many outlet way connections to be made.
  - Saddles - securing the conduit to surface during installation.
  - Elbow joint bend - to enable 90° bend to be made.
    Accept any other accessory
2. Faulty fluorescent fitting
  - Lamp does not light at all
  - Faulty starter switch.
  - No power supply.
  - Broken tube electrodes.
  - Broken wires in the circuit.
  - Burn out tube.
    Any 2 x1 = (3 marks)
3. 1. IEE Regulation
    - The rating of fuse or circuit breaker should be 30 A.
    - Maximum floor area should be 100 m2
    - Standard 13 A socket outlets should not be installed inside a
      bathroom.
    - The total number of spurs on stationary appliances shall not exceed the total number of socket outlets. Any 4x1 = (4 marks)
  2. Correct circuit - 2
    Components 6 x ½=3
    5 marks
1. Parts of a DC machine.
  1. Yoke
    Consists of the external frame (1) it forms part of the field
    magnetic circuit
    It is made of mild steel casing (1) or cast steel construction. 2 marks
  2. Poles
    They designed to produce the maximum flux in cores slots,
    each pole assembly is made up of a pole core circular or
    (1) rectangular threaded to a field coil.
    The core is bolted to the yoke and has an extension consisting of pole shoe. (1).
    marks
2. 1. KVA= I₁V₁ = I₂V₂
    100,000 = I₁ = 9.09A
    11000
  2. V₁ = N₁
    V₂ N₂
    (1) (1)
    N₂ = N₁ x V₂   = 800 x 240 = 17.45 tums
      V₁ 11000
    (3 marks)
    = 11000
    (c)
3. IEE Regulations
  1. Transformer must be double wound.
  2. The core of transformer (metal case at one point of the secondary
    must be earthed.
  3. The transformer must be connected to a separate sub-circuit
  4. Cables used to supply the transformer must be of suitable grade.
    Any 3x1 = (3 marks)
1. 1. NAND gate
    
    (1 mark)
  2. NOR gate
    
    (1 mark)
  3. OR gate
    
    (1 mark)
2. R_B = 100Ω R_L=IΩ Vcc = 10v
  I_B = Vcc = 10 = 0.1A
  R_B 100
  Ic = β = Ic = 100 x 0.1 = 10A
  I_B
  V_CE = V_cc- 1_cI_R = 10 - 10 x 1 = 0
3. 1. I_B = Vcc = 20 = 0.2A
    R_B 100
  2. IC = βI_B = 100 x 0.2=20A
  3. V_ce =V_cc - I_CI_R
    = 20 {(20)(2)}=-20 V
    (1% marks)
    191
Faces ABCDE = 5
Faces FGHIJK = 5½
Isometric = ½
Placement of X = ½
Correct measurements = 1
Neatness= ½
Line work= ½
Total = 13 marks