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BASIC ELECTRONICS July 2021

BASIC ELECTRONICS July 2021

Time: 3 hours

THE KENYA NATIONAL EXAMINATIONS COUNCIL

CRAFT CERTIFICATE IN INFORMATION TECHNOLOGY

BASIC ELECTRONICS 3 hours

INSTRUCTIONS TO CANDIDATES:

This paper consists of section A and B.
Answer ALL the 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)

  1. Outline four application areas of Gray code number systems.
    • Error correction in digital communications.
    • Minimizing errors in rotary encoders.
    • Simplifying digital circuit transitions.
    • Used in Karnaugh maps for logic simplification.
  2. Explain each of the following terms used in basic electronics:
    • Logic gate: A basic building block of digital circuits that performs logical operations such as AND, OR, NOT.
    • 8421 BCD (Binary-Coded Decimal): A binary representation where each decimal digit is encoded using four binary bits.
  3. With the aid of a symbol, describe a photodiode as used in electronics.
    • A photodiode is a semiconductor device that converts light into electrical current. It operates when light falls on it, allowing current to pass.
  4. Determine the hexadecimal equivalent of the following number systems:
    • (i) 001111₂ = 3F₁₆.
    • (ii) 0.0664062510 (requires more detailed conversion, typically done step-by-step).
  5. Describe two physical parts of an internal computer hard disk.
    • Platter: The disk that stores data, coated with magnetic material.
    • Read/Write Head: The component that reads and writes data on the platter.
  6. Differentiate between donor and acceptor atoms as applied in semiconductors.
    • Donor atoms: Atoms that add free electrons to a semiconductor, making it n-type.
    • Acceptor atoms: Atoms that create holes by accepting electrons, making the semiconductor p-type.
  7. Define each of the following terms as used in basic electronics:
    • Neutron: A neutral subatomic particle in the nucleus of an atom.
    • Conductivity: The ability of a material to conduct electric current.
    • Inductance: The property of a circuit or coil that opposes a change in current.
    • Impedance: The total opposition a circuit offers to the flow of alternating current.
  8. Determine the decimal equivalent of each of the following numbers:
    • 756₈ = 494₁₀.
    • 89.416₁₀ (already in decimal form).
  9. Explain the function of the parts labelled (i) and (ii) in Figure 1.
    • (i) (Assuming it’s a power source): Provides electrical energy.
    • (ii) (Assuming it’s a load): Consumes electrical energy.
  10. Explain two advantages of Excess-3 code.
    • It is self-complementary, simplifying arithmetic operations.
    • Reduces errors in digital transmission.

SECTION B (60 marks)

(Answers for selected questions)

  1. (a) (i) With the aid of a diagram, describe the depletion layer of a p-n junction.
    • The depletion layer is the region around the p-n junction where mobile charge carriers are depleted, forming a zone with immobile ions.

(ii) Distinguish between current and power as used in electronics. – Current refers to the flow of electric charge, measured in amperes (A). – Power is the rate at which electrical energy is consumed or produced, measured in watts (W).

  1. (a) (i) Trends of computer memory since the fourth generation:
    • Increased storage capacity.
    • Higher data transfer rates.
    • Reduced physical size of storage devices.
  2. (a) (i) Outline three disadvantages of using flash memory.
    • Limited write cycles, leading to eventual degradation.
    • More expensive than traditional hard drives.
    • Potential data loss if not properly managed.

(ii) Determine the resistance of the cable given:

  • Resistance (R) = Length (L) / (Conductivity (σ) × Cross-sectional Area (A)).
  1. (a) (i) Application areas of holographic memory:
    • High-capacity data storage.
    • Archival of large multimedia content.
    • Fast data retrieval systems.