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.
- 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. - 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. - 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% - Using one’s complement, work out 11100010 – 10110111:
Answer: 00101011 - 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.
- Outline four disadvantages of semiconductor components:
- Sensitive to temperature changes.
- Susceptible to radiation.
- Limited power capacity.
- Can be easily damaged by over-voltage.
- Convert the following numbers to their Gray code equivalent:
(i) 11112 – 1011
(ii) 10162 – 1111 - Determine the octal equivalent for each of the following number systems:
(i) 206 – 3168
(ii) 13910 – 2138 - 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. - 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.
- (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.
- 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. - List four types of resistors:
- Fixed resistors.
- Variable resistors.
- Thermistors.
- Light-dependent resistors (LDR).
- Convert the following numbers into their decimal equivalent:
(i) F07914516 – 251647181
(ii) 1010112 – 4310 - 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.
- Outline three factors affecting the resistance of a wire/conductor:
- Material of the conductor.
- Length of the wire.
- Cross-sectional area.
- Simplify the following Boolean algebra expression:
(i) (A + B)(A + C) = A + BC
(ii) AB + A(B + C) =A + BC
End of Paper