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BASIC ELECTRONICS JULY 2019

BASIC ELECTRONICS JULY 2019

Time: 3 hours

THE KENYA NATIONAL EXAMINATIONS COUNCIL

CRAFT CERTIFICATE IN INFORMATION TECHNOLOGY

INSTRUCTIONS TO CANDIDATES:

This paper consists of section A and B.
Answer ALL questions in Section A and any FOUR from Section B in the answer booklet provided. Candidates should answer the questions in English.

SECTION A (40 marks)

Answer ALL questions in this section.

  1. Describe two types of voltage regulators.
  • Linear voltage regulators: These regulators provide a stable output voltage with minimal noise but are less efficient due to energy loss as heat.
  • Switching voltage regulators: More efficient as they convert voltage using high-frequency switching, allowing better energy conservation and heat management.
  1. Convert the BCD number 0111 1000 to its Excess-3 equivalent.
  • BCD (0111 1000) = Decimal (78).
  • Excess-3 equivalent = Decimal (78) + 3 = Decimal (81) = 1000 0001.
  1. Differentiate between carbon-zinc batteries and alkaline batteries as used in electronics.
  • Carbon-zinc batteries: Lower cost, suitable for low-drain devices, shorter lifespan.
  • Alkaline batteries: Higher energy density, longer lifespan, suitable for moderate to high-drain devices.
  1. With the aid of a labeled sketch, outline the schematic symbol for a diode.
  • Answer: A diode symbol consists of a triangle pointing to a line (|<|), with the triangle representing the anode and the line representing the cathode.
  1. Explain two uses of extrinsic semiconductors.
  • Used in diodes to allow current to flow in one direction for rectification.
  • Used in transistors for amplification and switching in electronic circuits.
  1. Determine the binary equivalent of each of the following decimal numbers:
  • (i) 5 = 101₂.
  • (ii) 15 = 1111₂.
  1. List two disadvantages of using traditional computer storage media.
  • Limited storage capacity.
  • Slower data access speeds compared to modern SSDs.
  1. Draw the NOR gate equivalent using NOT gates and an OR gate.
  • Answer: An OR gate with its output connected to a NOT gate forms a NOR gate.
  1. Explain two circumstances of overflow during arithmetic operations of signed numbers.
  • When adding two positive numbers results in a negative result due to exceeding the range.
  • When subtracting a large negative number from a positive number produces an incorrect result.

SECTION B (60 marks)

Answer any FOUR questions from this section.

  1. (a) (i) Outline three types of inductors.
  • Air-core inductors: Used where minimal inductance is needed.
  • Iron-core inductors: Provide higher inductance, used in power supplies.
  • Ferrite-core inductors: Used in high-frequency circuits.

(ii) With the aid of sketches, sketch one complete wave cycle for each of the following waves:

  • Square wave (shows abrupt transitions between high and low).
  • Triangle wave (shows a linear increase and decrease).
  1. (a) (i) Outline three behaviors of valence electrons.
  • Form bonds to create molecules.
  • Can move to the conduction band under specific energy conditions.
  • Determine the electrical properties of a material.

(ii) Explain two quantities needed to determine the resistivity of a metal conductor.

  • Length of the conductor: Directly proportional to resistivity.
  • Cross-sectional area of the conductor: Inversely proportional to resistivity.
  1. (a) (i) List six resistor color codes used to determine resistance.
  • Black (0), Brown (1), Red (2), Orange (3), Yellow (4), Green (5).

(ii) Explain two drawbacks of using an external hard disk for the operating system.

  • Slower data access compared to internal drives.
  • Potential data corruption due to disconnections or movement.

(b) Convert the following hexadecimal numbers to their decimal equivalent:

  • (i) A8E₁₆ = 2702₁₀.
  • (ii) 9F07₁₆ = 40711₁₀.
  1. (a) (i) List six examples of Compact Disc (CD) memory types.
  • CD-ROM, CD-R, CD-RW, CD-DA, Video CD, Super Video CD.

(b) Perform the following BCD arithmetic:

  • I. 10011101 + 01101101:
    • Convert each to decimal (157 + 109), perform addition, convert back to BCD.
    • Result = 110010100 (BCD).
  • II. 10000110 + 10100111:
    • Convert each to decimal (134 + 167), perform addition, convert back to BCD.
    • Result = 100110101 (BCD).
  1. (a) Convert the following capacitance values as indicated:
  • I. 24 µF to F = 24 × 10⁻⁶ F.
  • II. 0.6 µF to F = 0.6 × 10⁻⁶ F.
  • III. 770 pF to F = 770 × 10⁻¹² F.

(b) Explain two challenges associated with the continuous evolution of computer memory.

  • Compatibility issues with older hardware/software.
  • Increased complexity in ensuring data security and integrity.

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