Electricity Paper 1 Questions and Answers - MECS Cluster Joint Mock Exam

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

1.      
   1. List four insulating materials used in electrical installations. (2 marks)
   2. State two advantages of mineral insulated copper sheathed cables over PVC sheathed. (2 marks)
2.      
   1. State Lenz’s law of electromagnetic induction. (2 marks)
   2. Name four applications of electromagnets. (2 marks)
3.      
   1. Name four National Polytechnics in Kenya. (2 marks)
   2. List two business opportunities in the field of electricity. (1 mark)
4.    
   1. State how each of the following electrical material waste should be disposed safely:
      
      1. Burnt fluorescent tubes; (½ mark)
      2. Damaged computers. (½ mark)
   2. State the application of each of the following types of extinguishers:
      
      1. Carbon dioxide; (1 mark)
      2. Water. (1 mark)
5. Figure 1 shows a carbon resistor with color codes. Determine the value of the resistor given, (2 marks)
   
6. Figure 2 shows a resistive circuit.
   
   Determine the:
   
   1. Value of the resistor B if the total circuit resistance is 20Ω; (4 marks)
   2. Total circuit current. (2 marks)
7.      
   1. Name four parts of a fluorescent fitting. (2 marks)
   2. List four marking out tools used in fabricating sheet metal casing. (2 marks)
8.      
   1. Figure 3 shows two views of an object drawn in third angle projection.
      
      On the grid provided, make a free hand isometric sketch with corner N as the lowest point. (3 marks)
      
   2. Outline two ways that can be used to troubleshoot a faulty television. (2 marks)
9.      
   1. With the aid of sketches, distinguish between P-N-P and an N-P-N transistor. (3 marks)
   2. Name four applications of a P-N junction diode. (2 marks)
10.        
    1. State three advantages of digital instruments over analogue instruments. (3 marks)
    2. An ideal transformer connected to a 240V mains supplies a 12V, 120W lamp. Calculate the:
       
       1. Transformer’s turns ratio; (3 marks)
       2. Current taken from the supply. (3 marks)
    3. With the aid of diagram describe 'armature reaction' in d.c motors (3mks)

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

11.      
    1.    
       1. Convert 2310 to binary. (2 marks)
       2. Convert 110112 to decimal. (2 marks)
    2.      
       1. State seven types of logic gate;(4 marks)
       2. Draw a truth table for the; NAND. (4 marks)
    3. Name two applications of logic gates. (1 mark)
12.        
    1. Draw a sine wave and indicate the following:
       
       1. Peak value; (5 marks)
       2. Instantaneous value;
       3. Cycle.
    2. Figure 4 shows an RLC circuit. The supply frequency is 50Hz
       
    3. Calculate the:
       
       1. Inductive reactance; (2 marks)
       2. Capacitive reactance; (2 marks)
       3. Circuit impedance; (2 marks)
       4. Circuit current. (2 marks)
13.      
    1. State;
       
       1. Two advantages of a moving coil instrument. (2 marks)
       2. Two essential features of an analogue instrument. (2 marks)
    2. With the aid of a labelled diagram, explain the Flemmings right hand rule to demonstrate the direction of induced EMF. (6 marks)
    3. show that for two capacitors C1 and C2 connected in series, the total capacitance is given by:
       C_T = C1 × C2 (3 marks)
                C1+C2 
14.         
    1. State:
       
       1. Two advantages of trunking over steel conduit wiring systems. (2 marks)
       2. Two advantages of MCBs over rewirable fuses. (2 marks)
    2.      
       1. Draw and label a diagram of a switch start fluorescent fitting. (6 marks)
       2. Outline three tests carried out in a completed electrical installation. (3 marks)
15. Figure 5 shows a machine block drawing of an isometric projection.
    
    Draw the following views in full size in first angle projection:
    
    1. Front elevation in the direction of arrow F:
    2. Plan;
    3. Indicate six dimensions. (13 marks)

MARKING SCHEME

1.    
   1.      
      • PVC
      • bakelite
      • Polychloroprene
      • rubber
   2. It is the cheapest system
      It is easy and quick to install
      P.v.c. is impervious to many chemicals and free from ageing
2.        
   1. The direction of induced emf is such that itopposes the change that causes it
   2. DC machines
      AC machines
      Measuring instruments
      Moving coil loud-speaker
3.      
   1. Eldoret, kabete, Kisumu, Meru, Nyeri
   2. Electrical/ Electronics parts seller
      Electronics repair shop
      Electronics waste disposal
      Cyber café shop
4.      
   1.    
      1. Burnt fluorescent tubes; (½ mark)
         Take to hazardous waste collection centre
      2. Damaged computers. (½ mark)
         Donated to community as second or third grade computers
   2.      
      1. Carbon dioxide; (1 mark)
         Extinguish electric fires
      2. Water.
         Extinguish solid fuel and fluid fuel fires (1 mark)
5. 10 x 10² ± 5%
   1KΩ
6.      
   1. 10+12xB=20
            12+B
      2B=120
      B=60Ω
   2. I = ^Vs/_Rt
      ²⁰/₂₀=1A
7.      
   1. Starter
      Electrodes
      Tube
      choke
   2. Scriber
      Steel rule
      dividers
      try square
      centre punch
8.      
   1. On the grid provided, make a free hand isometric sketch with corner N as the lowest point. (3 marks)
   2. Test working of fuse plug
      Test capacitor at the input
9.    
   1.      
   2. Power rectification
      In smoothing circuits
      In photo diodes
      In light emitting diodes
      In zener diodes
10.      
    1. Easy to read
       More accurate
       Less expensive
    2. Transformer’s turns ratio; (3 marks)
       ^V1/_V2 = ²⁴⁰/12=20
       Current taken from the supply. (3 marks)
       ^V1/_V2 = ^I1/_I2 
       I₁ = ¹²/₁₂₀ x 10 =1A
    3. This is the distortion and weakening of the main magnetic field in a dc machine due the field’s reaction with the armature’s magnetic flux.
       
11.      
    1.    
       1. 111₂
       2. 27₁₀
    2.    
       1. NOT gate, OR gate ,AND gate,NOR gate, the NAND gate, the XOR gate and the XNOR gate.
       2.    
          
          

          A	B	F
          0 0 1 1	0 1 0 1	1 1 1 0

    3. In burglar alarms
       As switches
       For computation analysis in circuits
12.      
    1.    
       
    2.    
       1. XL = 2πfL= 2π x 50 x 0.15 = 47.1Ω
       2. X_c =   1    =         1           31.831Ω
                 2πfc  2πx50x100µF
       3. Z=√(R²) + (X_L - X_C) √144+233.14=377.14Ω
       4. I = ^Vs/_Z = ²⁰⁰/_377.14 = 0.530A
13.      
    1.      
       1. It is shielded from magnetic fields
          Inexpensive compared to moving iron meters
          Have uniforn scale
       2. Controlling feature
          Damping feature
          Deflecting feature
    2.    
       
    3. ¹/_Ct = ¹/_C1 + ¹/_C2 = ^C1+C2/_C1C2 = C_t = ^c1c2/_c1+c2
14.        
    1.      
       1. cables are laid in rather than pulled in.
          can take large number of cables
       2. Can be reset after rectifying fault
          Faulty circuit is indicated by MCB
          Can be used as a switch
    2.      
       1.      
          
       2. Earthing tests
          Ring circuit continuity test
          Insulation resistance tests
          Verification of polarity tests 
15. 
    
    Solution-3mks mks
    Accuracy-3mks
    Neatness-2mks
    Dimensions-4mks
    Borderline-1mk