INSTRUCTIONS TO CANDIDATES
 The paper contains two sections: Section A and Section B
 Section A carries 52 marks while section B carries 48 marks
 Answer ALL the questions in section A and ANY FOUR questions in section B
 All the answers and working must be written on the question paper in the spaces provided below each question.
 Nonprogrammable silent electronic calculators are allowed for use
SECTION A (52 Marks)
Answer all questions

 Name four prime movers used in the process of generation electricity in Kenya (2 marks)
 State two responsibilities of the following job groups (2 marks)
 Artisan
 Technician

 State four main components of a business plan (2 marks)
 State four causes of electric shock in a workshop (2 marks)

 State two safety precaution that needs to be put in place to avoid accidents from overhead power lines (2 marks)
 Draw a common base transistor configuration circuit (1 mark)
 The figure 1 shows a logic gate
 Give the name of the logic gate (1 mark)
 Draw the truth table for the logic gate shown (2 marks)

 Differentiate between a conductor and a semiconductor. (1 mark)
 State one area of application for each of the above materials (2 marks)
 State four uses of ohmmeter function of a multimeter in trouble shooting circuits (2 marks)

 Using a schematic diagram, show how a lamp can be controlled from two different position (2 marks)
 Find the resistance of a resistor whose color code is: (2 marks)
 Grey, Red, Gold, Gold
 Green, White, Black, Gold
 With aid of a diagram, differentiate between repulsion and attraction type moving iron meter (4 marks)
 A single phase stepdown transformer has a ratio of 8:1, a primary voltage of 3.3kV and a load of 6.6kVA. Ignoring losses, calculate; (6 marks)
 Secondary voltage
 Secondary current
 Sketch the symbol for the following circuit symbol (2 marks)
 Zener diode
 Incandescent lamp

 State the meaning of capacitance (1 mark)
 State three factors that affect the capacitance of a capacitor (3 marks)

 What is an autotransformer (1 mark)
 An autotransformer has 1200 turns connected to 250V a,c to supply a 60V load. Calculate the number of turns in the secondary section (2 marks)

 Three inductors of 60mH, 120mH and 75mH respectively, are connected together in a parallel combination. Calculate the total inductance of the parallel combination (1 mark)
 Find the total energy in the circuit given that the total current is 2.5A. (2 marks)

 State three parts of a machine (marks)
 An alternating current completes ten cycles in 0.1 seconds. Calculate the period and frequency of the current. ()
 In a 12V dc system a 40W solar panel is exposed to the sun for six hours daily. Calculate the number of days it will take to fully charge a 60 amperehour battery (4 marks)
SECTION B (48 Marks)
Answer any four questions
 Figure 2 shows and RLC circuit. (12 marks)
Calculate the: Inductive reactance
 Capacitive reactance
 Circuit impedance
 Circuit current
 Power dissipated in the circuit

 With aid of a labelled diagram, explain the principle of operation of a trembler bell. (9 marks)
 With aid of a diagram, differentiate between shunt generator and series d.c generator (3 marks)
 Figure 3 shows the isometric view of a towing hook.
Draw, full size, in third angle projection: (12 Marks) front elevation in the direction of arrow A;
 end elevation in the direction of arrow B

 With reference to Sinusoidal waveforms, explain each of the following terms (3 marks)
 Amplitude
 Period
 Frequency
 A Sinusoidal voltage trace displayed on an oscilloscope has peak voltage of 48V and a period of 80 ms. (9 marks)
Draw the waveform and calculate: Frequency
 Average value
 RMS value
 With reference to Sinusoidal waveforms, explain each of the following terms (3 marks)

 Explain why a series motor develops high torque when subjected to a heavier load(5 marks)
 A 240V/120V, 1.2kVA transformer delivers power to a load. Calculate the:
 Transformation ratio
 Rated secondary current
 Primary impedance at the rated load
 Number of turns in secondary winding if the primary winding induces 0.2V per turn (7 marks)
Marking Scheme

 Name four prime movers used in the process of generation electricity in Kenya(2 marks)
 Wind turbine
 Gas turbine
 Hydroturbine
 Steam turbine
4x½=2 marks
 State two responsibilities of the following job groups (2 marks)
 Artisan
 Perform skilled electrical work
 Plant maintenance
 Repair of electrical equipment
 Control and modifying circuit
Any 2x½=1 marks
 Technician
 To organize and manage workshop accordingly
 To participate in the decision making process at the middle level management
 To supervise, organize and instruct the work under them
Any 2x½=1 marks
 Artisan
 Name four prime movers used in the process of generation electricity in Kenya(2 marks)

 State four main components of a business plan (2 marks)
 Self confident
 Optimistic
 Action oriented
 Futuristic
 Achievement motivation
 Respond positively to challenges
4x½=2 marks
 State four causes of electric shock in a workshop (2 marks)
 Carelessness
 Poor electric circuit condition
 Fatigue
 Working under the influence of impairing substance such as alcohol
 Incompetence in handling electric circuits
Any 4x½=2 marks
 State four main components of a business plan (2 marks)

 State four safety precaution that needs to be put in place to avoid accidents from overhead power lines (2 marks)
 Never attempt to climb electric power posts
 Avoid climbing trees near overhead power lines
 Do no throw objects at the power lines.
 Do not erect buildings below power lines
 Do not set fire near power line posts
Any 4x½=2 marks
 Draw a common base transistor configuration circuit (1 mark)
1x1=1 mark
 State four safety precaution that needs to be put in place to avoid accidents from overhead power lines (2 marks)
 Figure 1 shows a logic gate
 Give the name of the logic gate (1 mark)
 NAND gate
 Draw the truth table for the logic gate shown (2 marks)
INPUT OUTPUT A B Z 0 0 1 0 1 1 1 0 1 1 1 0
Output binary 1 mark
Total = 2 marks
 Give the name of the logic gate (1 mark)

 Differentiate between a conductor and a semiconductor. (1 mark)
 A conductor is a material that has many free electrons and allows electric current to flow through them.
 A semiconductor is a material that is a poor conductor at low temperature and good conductors at high temperatures.
2 x ½=1 mark
 State one area of application for each of the above materials (2 marks)
 Conductors power transmission and distribution, electronic devices such as radios, domestic installation e.t.c
 Semiconductors manufacture of diodes and integrated circuits, solar technology e.t.c
1 x 2=2 marks
 Differentiate between a conductor and a semiconductor. (1 mark)
 State four uses of the ohmmeter function of a multimeter in trouble shooting circuits (2 marks)
 Testing for open circuits
 Ascertaining polarities of diodes and transistors
 Checking short circuits
 Checking continuity of heating elements and motor winding.
 Identifying defective components
Any 4 x ½=2 marks

 Using a wiring diagram, show how a lamp can be controlled from two different position (2 marks)
switch connected to live=1 mark
L2 to L2 and L1 to L1 connection=1 mark
Total= 2marks  Find the resistance of a resistor whose color code is;
 Grey, Red, Gold, Gold
82 x 0.1 ± 5% = 8.2 ± 5%Ω
1 mark  Green, White, Black, Gold
59 x 10º ± 5% = 59 ± 5%Ω
1 mark
Total (2 marks)
 Grey, Red, Gold, Gold
 Using a wiring diagram, show how a lamp can be controlled from two different position (2 marks)
 With aid of a diagram, differentiate between repulsion and attraction type moving iron meter (4 marks)
Repulsion type moving iron instrument consists of two vanes whereby one vane in stationary the other is fastened to the pivot which carries the pointer and the control spring.
The meter uses soft iron plunger projecting partway into the stationary field coil. The current in the field coil produces a magnetic force which pulls the plunger further into the coil.  A single phase stepdown transformer has a ratio of 8:1, a primary voltage of 3.3kV and a load of 6.6kVA. Ignoring losses, calculate; (6 marks)
 Secondary voltage
voltage ratio = Vp/Vs = 81
Vs = Vp/8 = ^{3300}/_{8 }= 412.5V  Secondary current
Is = VpIps = ^{6.6 x 1000}/_{412.5} = 16A
 Secondary voltage
 Sketch the symbol for the following circuit symbol (2 marks)
 Zener diode
 Incandescent lamp
 Zener diode

 State the meaning of the term capacitance (1 mark)
 This the property of a circuit which opposes any changes in circuit voltage
 State three factors that affect the capacitance of a capacitor (3 marks)
 Area of the capacitor plates
 Distance between the plates
 The material of the dielectric
3x1=3 marks
 State the meaning of the term capacitance (1 mark)

 What is an autotransformer (1 mark)
 It is a type of transformer that has its secondary winding tapped from the primary winding
 Its primary and secondary winding is not electrically insulated from each
Any 1x1=1 mark
 An autotransformer has 1200 turns connected to 240V a,c to supply a 60V load. Calculate the number of turns in the secondary section (2 marks)
 ^{Vp}/_{Vs}=^{Np}/_{Ns}
Ns=^{NpNs}/_{Vp}
Ns=^{1200 x 60}/_{240}=300 turns
 ^{Vp}/_{Vs}=^{Np}/_{Ns}
 What is an autotransformer (1 mark)

 Three inductors of 60mH, 120mH and 75mH respectively, are connected together in a parallel combination. Calculate the total inductance of the parallel combination (1 mark)
 1/L_{T}= ^{1}/_{60} + ^{1}/_{120} + ^{1}/_{75} = ^{23}/_{600}
LT=^{600}/_{23}
=26.09mH
 1/L_{T}= ^{1}/_{60} + ^{1}/_{120} + ^{1}/_{75} = ^{23}/_{600}
 Find the total energy in the circuit given that the total current is 2.5A. (2 marks)
 E=^{1}/_{2}LI^{2}=^{1}/_{2} x 26.09 x 10^{3} x 2.5^{2}
=0.0815 joules
 E=^{1}/_{2}LI^{2}=^{1}/_{2} x 26.09 x 10^{3} x 2.5^{2}
 Three inductors of 60mH, 120mH and 75mH respectively, are connected together in a parallel combination. Calculate the total inductance of the parallel combination (1 mark)

 State three parts of a machine (112 marks)
 Stator
 Rotor
 Commutator
 Frame
 End Shield
3 x ^{1}/_{2}=1^{1}/_{2} marks
 An alternating current completes ten cycles in 0.1 seconds. Calculate the period and frequency of the current. (1^{1}/_{2} marks)
10 cycles=0.1 sec
1 sec
period = ^{1 x 0.1}/_{10}=0.01sec
Frequency=^{1}/_{T}=^{1}/_{0.01}=100 H
 State three parts of a machine (112 marks)
 In a 12V dc system, a 40W solar panel is exposed to the sun for six hours daily. Calculate the number of days it will take to fully charge a 60 amperehour battery (4 marks)
Current for the solar panel, I= 40/12=3.3333A
∴rate of charge=3.3333 x 6=20Ah
No. of days required for full charge is;
^{60Ah}/_{20Ah}=3 days  The figure below shows and RLC circuit.
Calculate the: Inductive reactance
 XL=2πfL
=2 x π x 50 x 0.4
=125.6Ω
 XL=2πfL
 Capacitive reactance
 XC=^{1}/_{2πfC}
= 1
2 x π x 50 x 50 x 10^{6}
=63.7Ω
 XC=^{1}/_{2πfC}
 Circuit impedance
 Z= √R^{2}+(X_{L}X_{C})^{2}
 =502+(125.763.7)^{2}
=79.6Ω
 Circuit current
 I=^{V}/_{Z}
=^{240}/_{79.6}
=3A
 I=^{V}/_{Z}
 Power dissipated in the circuit
 Power=I^{2}R
=3^{2 }x 50
=450W
(12 marks)
 Power=I^{2}R
 Inductive reactance

 With aid of a labelled diagram, explain the principle of operation of a trembler bell. (9 marks)
 When the push button is pressed, current flows through the circuit.
 The coil becomes energized and attracts the armature which is attached to the striker hence strikes the gong. The armature moves away from the contact screw breaking the contact.
 The coils are deenergized and the armature falls back to its original position and its circuit is completed once again.
 The sequence of movement recurs causing a continuous trembling sound.
 With aid of a diagram, differentiate between shunt generator and series d.c generator (3 marks)
 DC Shunt generator
 DC shunt field winding consists of high resistance coils which are made of a large number of turns of insulated copper wire.
 The field winding is connected in parallel (shunt) with the armature. (any 1x1=1 mark)
 DC Series generator
 It has its field winding connected in series with the armature winding.
 The windings are made of few turns of copper wire.
 It does not build up the field if it is started with the external circuit open. (any 1x1=1 mark)
 DC Shunt generator
 With aid of a labelled diagram, explain the principle of operation of a trembler bell. (9 marks)
 The figure below shows the isometric view of a towing hook.
Draw, full size, in third angle projection: front elevation in the direction of arrow A;
 end elevation in the direction of arrow B (12 marks)
Hidden details=1
First angle projection= 1
Neatness=1
Total =12 Marks

 With reference to Sinusoidal waveforms, explain each of the following terms (3 marks)
 Amplitude
 Is the maximum value, positive or negative of an alternating quantity
 Period
 Is the time taken by an alternating quantity to complete one cycle
 Frequency
 Is the number of cycles of an alternating quantity completed in a circuit
 Amplitude
 A Sinusoidal voltage trace displayed on an oscilloscope has peak voltage of 48V and a period of 80 ms. (9 marks)
Draw the waveform and calculate:
Axes  1
Peak values  1
Wave Form  1
Period  1
4 marks Frequency
 f=^{1}/_{T}= 1 =12.5 Hz
80x10^{3}
 f=^{1}/_{T}= 1 =12.5 Hz
 Average value
 V_{av}=0.637xV_{max}
=0.637x48
=30.576V
 V_{av}=0.637xV_{max}
 RMS value
 V_{rms}=0.707xV_{max}
=0.707x48
=33.94V
 V_{rms}=0.707xV_{max}
 Frequency
 With reference to Sinusoidal waveforms, explain each of the following terms (3 marks)

 Explain why a series motor develops high torque when subjected to a heavier load (5 marks)
 Assuming the motor has been operating at moderate speed, when it is suddenly subjected to heavier load, the first effect is to slow down the motor.
 Slowing the motor reduces back e.m.f generated since back e.m.f is directly proportional to speed.
 Reduced back e.m.f makes the line voltage to push more current through the motors field coils
 More current in the field coils produces a stronger magnetic field
 Because torque depends on the product of both magnetic field and flux, both will therefore increase and so will the torque.
(Any 5x1 =5 marks)
 A 240V/120V, 1.2kVA transformer delivers power to a load. Calculate the: (7 marks)
 Transformation ratio
 Transformer ratio=^{Vp}/_{Vs}=^{240V}/_{120V}=2
 Rated secondary current
 I_{S}=^{KVA}/_{Es}=^{1200}/_{120}=10A
 Primary impedance at the rated load
 Primary impedance=a^{2}Z_{L}
Secondary impedance=^{120}/_{10=}12Ω
a=z ∴ Z_{P}=2^{2}x12=48Ω
 Primary impedance=a^{2}Z_{L}
 Number of turns in secondary winding if the primary winding induces 0.2V per turn
 =^{Es}/_{Rate per turn }= ^{120}/_{0.2} = 600 turns
 Transformation ratio
 Explain why a series motor develops high torque when subjected to a heavier load (5 marks)
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