ELECTRICITY AND ELECTRONICS

Maximum Marks: 80
Time Allotted: Three Hours
Reading Time: Additional Fifteen minutes

Instructions to Candidates

1. You are allowed an additional fifteen minutes for only reading the question
paper.
2. You must NOT start writing during the reading time.
3. This question paper has 8 printed pages.
4. It is divided into three sections and has thirteen questions in all.
5. All questions are compulsory.
6. Section A has twelve subparts which are very short answer questions.
Each subpart carries 1 mark.
7. While attempting Multiple Choice Questions in Section A, you are required
to write only ONE option as the answer.
8. Section B has eight questions which are short answer questions.
Each question carries 4 marks.
9. Section C has four questions which are long answer questions.
Each question carries 8 marks.
10. Internal choices have been provided in two questions in Section B and in
one question in Section C.
11. The intended marks for questions are given in brackets [ ].
Instruction to Supervising Examiner
1. Kindly read aloud the Instructions given above to all the candidates present
in the examination hall.

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 SECTION A – 16 MARKS
Question 1
(i) Which one of the following parts of the Cathode Ray Oscilloscope (CRO) is used to [1]
control the path of the electron beam?
(a) Accelerating anode
(b) Horizontal and vertical deflection plates
(c) Electron gun
(d) Cathode
(ii) The effect of demagnetisation component of armature reaction in a d.c. generator: [1]
(a) causes commutation in the armature coil.
(b) leads to constant copper loss.
(c) creates distortion in the magnetic field.
(d) weakens the main magnetic flux.
(iii) The back emf of a d.c. motor: [1]
(a) adds to the supply voltage.
(b) regulates its armature voltage.
(c) helps in energy conversion.
(d) usually exceeds the supply voltage.
(iv) The load characteristics shown in Figure 1 and Figure 2 below are respectively [1]
of: V0 V
0

IL IL
Figure 1 Figure 2
(a) Series d.c. generator, Shunt d.c. generator
(b) Shunt d.c. generator, Series d.c. generator
(c) Series d.c. motor, Shunt d.c. motor
(d) Shunt d.c. motor, Series d.c. motor

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 (v) An efficient amplifier has _____________ input resistance and _____________ [1]
output resistance.
(a) high, low
(b) high, high
(c) low, low
(d) low, high
(vi) An electric fuse works on the _____________. (heating effect of current, chemical [1]
effect of current)
(vii) If the peak value of an alternating current is 4A, then the rms value of the current [1]
4
will be _____________. ( , 4√2)
√2

(viii) A single-phase induction motor can be made a self-starting machine by using a [1]
_____________. (capacitor, diode)
(ix) The working of a crystal microphone is based on _____________. [1]
(Piezoelectric effect, Electromagnetic induction)
(x) Name a device that can be used to convert 12V a.c. to 200V a.c. [1]
(xi) Match the devices given in Column I with their correct functions given in [4]
Column II.
Column I Column II
1. A. Amplifies both current and voltage

2. Anode Cathode B. Amplifies voltage and reduces current

(+) (-)

3. C C. Changes a.c voltage and current to

pulsating d.c. voltage and current
B

E
4. Anode Cathode D. Maintains constant voltage even with
(+) (-) variation in current

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 (xii) State whether the following are True or False:
(a) An electric generator works on the principle of electromagnetic induction. [1]
(b) A wire with a green insulation is usually the live wire of an electric supply. [1]

SECTION B - 32 MARKS
Question 2 [4]
With the help of a neat circuit diagram, explain the working of a split phase a.c. motor.

Question 3 [4]
Draw a neatly labelled circuit diagram of a half wave rectifier using a semiconductor
diode. Also, sketch its output graph.

Question 4 [4]
Explain the working of a moving coil loudspeaker.

Question 5 [4]
Draw a neatly labelled circuit diagram of a triode that works as a voltage amplifier.

Question 6 [4]
Explain the working of a 𝝅 − 𝒔𝒆𝒄𝒕𝒊𝒐𝒏 filter.

Question 7 [4]
Figure 3 below shows the circuit diagram of a voltage regulator. Answer the following
questions.
Rs Is = 10A
+ +
IZ IL = 6A

Vin 80V VZ 60V RL

- -
Figure 3
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 (i) What is the Zener voltage?
(ii) Calculate the Zener current.
(iii) What is the voltage across the series resistor Rs?
(iv) Calculate the resistance of the load.

Question 8 [4]
(i) Draw a circuit diagram of a Vacuum Tube Voltmeter (VTVM).
OR
(ii) Draw a circuit diagram of a multimeter that can be used as an ammeter.

Question 9 [4]
(i)

Image 1 Image 2

Image 1 and Image 2 show distribution of power using cables.

(i) State any two advantages of cables used in Image 1 as compared to cables
used in Image 2.
(ii) State any two ways to minimise losses in a transformer.
OR

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 (ii) Figure 4 and Figure 5 below show a network of distribution of power.
Study them carefully and answer the questions that follow:
1

√3𝑉 𝑉 √3𝑉
S √3𝑉 S
2
𝑉
3
√3𝑉 √3𝑉
4
Figure 4 Figure 5

(a) Identify Figure 4 and Figure 5.

(b) What is the colour of insulation for wire 2 represented in Figure 5?
(c) Name any one live (phase) wire which carries current in Figure 5.

SECTION C - 32 MARKS

Question 10
(i) Identify the types of cables shown in Image 3 and Image 4. State any two [4]
advantages of the cable shown in Image 4 over the one in Image 3.

Image 3 Image 4
(ii) (a) Draw a neat circuit to show how a dual switch operates in staircase lighting. [2]
(b) Where are the switches and fuses located in an electrical circuit? [2]

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 Question 11
(i) Draw a neat diagram of a power amplifier. Also, name the coupling device used [5]
for impedance matching.
(ii) Figure 6 given below shows a transistor amplifier. [3]

IC
Vi
RL

VEB VCB

Figure 6
(i) Write the current equation for the transistor.
(ii) Identify the mode of connection of the transistor in the circuit.
(iii) Define current amplification factor for the circuit.

Question 12
(i) A shunt generator delivers 450A at 230V. The resistance of the shunt field and that [4]
of the armature are 50Ω and 0·03Ω respectively. Calculate the generated emf (Eg).
(ii) Sketch a graph of no-load characteristic of a shunt generator. [2]
(iii) Draw a neat circuit diagram of a series generator. [2]
OR
(i) A 120V d.c. shunt motor draws a current of 200A. The armature resistance is [4]
0·02Ω, and shunt field resistance is 30Ω. Calculate the back emf (Eb).
(ii) Draw a neat circuit diagram of a series motor. [2]
(iii) Sketch a graph of speed versus torque for a series motor. [2]

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 Question 13
(i) With reference to transistors, obtain the relationship between current amplification [4]
factors α and β (where symbols have their usual meaning).
(ii) Explain the working of a forward biased diode. Also, sketch a graph of [4]
current versus voltage in a forward biased condition.

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