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)
- 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.
- 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.
- 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.
- Determine the hexadecimal equivalent of the following number systems:
- (i) 001111₂ = 3F₁₆.
- (ii) 0.0664062510 (requires more detailed conversion, typically done step-by-step).
- 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.
- 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.
- 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.
- Determine the decimal equivalent of each of the following numbers:
- 756₈ = 494₁₀.
- 89.416₁₀ (already in decimal form).
- 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.
- 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)
- (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).
- (a) (i) Trends of computer memory since the fourth generation:
- Increased storage capacity.
- Higher data transfer rates.
- Reduced physical size of storage devices.
- (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)).
- (a) (i) Application areas of holographic memory:
- High-capacity data storage.
- Archival of large multimedia content.
- Fast data retrieval systems.