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BASIC ELECTRONICS – November 2021

Time: 3 hours

THE KENYA NATIONAL EXAMINATIONS COUNCIL
CRAFT CERTIFICATE IN INFORMATION TECHNOLOGY
BASIC ELECTRONICS

INSTRUCTIONS TO THE CANDIDATE

This paper consists of Section A and Section B.

• Answer ALL questions in Section A and ANY FOUR questions from Section B.
• Candidates should answer the questions in English.

SECTION A (40 Marks)

Answer ALL questions in this section.

1. Define each of the following terms used in basic electronics:
   (i) Transformer – A device that transfers electrical energy between two or more circuits through electromagnetic induction.
   (ii) Load – An electrical component or portion of a circuit that consumes electric power.
   (iii) Electron – A subatomic particle with a negative electric charge.
   (iv) Resistance – The opposition that a substance offers to the flow of electric current.
2. Explain each of the following terms as used in logic electronics:
   (i) Error clock – A signal used in digital electronics to correct timing or synchronization errors.
   (ii) NOT gate – A logic gate that outputs the opposite value of its input.
3. Determine the resistance of each of the following resistor’s color codes (Magnitude):
   (i) Red, black, yellow, gold – 200kΩ ± 5%
   (ii) Purple, green, blue, silver – 75.6MΩ ± 10%
4. Using one’s complement, work out 11100010 – 10110111:
   Answer: 00101011
5. Explain two characteristics of Read-Only Memory (ROM):

• Non-volatile: Retains data when power is turned off.
• Pre-programmed: Data stored during manufacturing or writing processes.

6. Outline four disadvantages of semiconductor components:

• Sensitive to temperature changes.
• Susceptible to radiation.
• Limited power capacity.
• Can be easily damaged by over-voltage.

7. Convert the following numbers to their Gray code equivalent:
   (i) 11112 – 1011
   (ii) 10162 – 1111
8. Determine the octal equivalent for each of the following number systems:
   (i) 206 – 3168
   (ii) 13910 – 2138
9. Explain each of the following terms as used in number systems:
   (i) Logical shift – A bitwise operation that shifts bits to the left or right, filling with zeros.
   (ii) Binary mask – A bit pattern used to select specific bits from another bit pattern.
10. With the aid of a diagram, describe the N-type semiconductors:
    Answer: N-type semiconductors are created by doping pure silicon or germanium with a pentavalent element, introducing extra electrons as charge carriers.

SECTION B (60 Marks)

Answer ANY FOUR questions from this section.

11. (a) (i) Evaluate the following octal arithmetic, 6418 × 138:
    Answer: 107888

(ii) Differentiate between an ammeter and a voltmeter:

• Ammeter: Measures current in amperes.
• Voltmeter: Measures voltage in volts.

12. Figure 1 shows an AC circuit. State the function of the parts labeled (i) and (ii):
    (i) Capacitor – Stores electrical energy in an electric field.
    (ii) Inductor – Stores energy in a magnetic field.
13. List four types of resistors:

• Fixed resistors.
• Variable resistors.
• Thermistors.
• Light-dependent resistors (LDR).

14. Convert the following numbers into their decimal equivalent:
    (i) F07914516 – 251647181
    (ii) 1010112 – 4310
15. Differentiate between reverse bias and forward bias as used in semiconductor diodes:

• Reverse bias: Increases the depletion region, preventing current flow.
• Forward bias: Reduces the depletion region, allowing current flow.

Explain two circumstances that necessitate the use of NAND gates in circuits:

• To simplify circuit design.
• To implement universal logic functions.

16. Outline three factors affecting the resistance of a wire/conductor:

• Material of the conductor.
• Length of the wire.
• Cross-sectional area.

17. Simplify the following Boolean algebra expression:
    (i) (A + B)(A + C) = A + BC
    (ii) AB + A(B + C) =A + BC

End of Paper