Module III Mock Examination 2 — Electromagnetic Fields and Communication Systems — Questions Only

Practice notice: This is an original KNEC-style revision mock based on the structure, command words, mark balance and difficulty of the supplied Module III paper. It is not an official KNEC examination paper.

INSTRUCTIONS TO CANDIDATES

1. This paper has two sections: Section A and Section B.
2. Answer any TWO questions from Section A and any THREE questions from Section B.
3. All questions carry 20 marks. Attempt all parts of each selected question.
4. Show all working for calculations, use appropriate units and draw clear labelled diagrams.
5. Use a non-programmable scientific calculator where necessary. Take c = 3 × 10⁸ m/s, η₀ = 120π Ω and μ₀ = 4π × 10⁻⁷ H/m.

SECTION A: ELECTROMAGNETIC FIELDS THEORY

Attempt any TWO questions from this section.

QUESTION 1 (20 marks)

(a) State Coulomb’s law of electrostatics. (2 marks)

(b) Two equal positive point charges of 20 μC each are located in free space at (−3, 0, 0) and (3, 0, 0). Determine the electric field at (0, 4, 0) and the force on a −10 μC charge placed at that point. (10 marks)

(c) State three co-ordinate systems used in electromagnetic field analysis. (3 marks)

(d) A magnetic material has relative permeability 6 and is in a magnetic field strength of 15 A/m. Determine its magnetic flux density and magnetization. (5 marks)

QUESTION 2 (20 marks)

(a) State Biot–Savart law. Points P₁ = (1, 2, 0) and P₂ = (4, 6, 0) are associated with a current element of 5πaz μA·m at P₁. Determine the unit vector from P₁ to P₂ and the incremental field strength at P₂. (11 marks)

(b) State Maxwell’s equations in integral form for time-varying fields. (4 marks)

(c) State five desirable properties of dielectric materials. (5 marks)

QUESTION 3 (20 marks)

(a) A uniform plane wave in free space has electric field E = 60 cos(ωt + 12z)ax V/m. Determine the angular frequency, wavelength, magnetic field intensity and average power density. (8 marks)

(b) A wave crosses an interface at z = 0. In medium 1, μr1 = 2 and B₁ = (2ax + 1.5ay + 0.8az) T. In medium 2, μr2 = 6. With no free surface current, determine the angle made by B₁ with the normal and the expression for B₂. (8 marks)

(c) State two sources of electromagnetic radiation and two properties of electromagnetic waves in free space. (4 marks)

SECTION B: COMMUNICATIONS SYSTEMS

Attempt any THREE questions from this section.

QUESTION 4 (20 marks)

(a) State three merits of digital radar systems. (3 marks)

(b) Draw a labelled block diagram of a continuous-wave Doppler radar and describe its operation. (8 marks)

(c) A 1.2 GHz pulsed radar produces a minimum received power of 500 pW at 20 km. The antenna capture area is 6 m² and the target cross-sectional area is 12 m². Determine the peak pulsed power radiated and the minimum received power at 35 km. (9 marks)

QUESTION 5 (20 marks)

(a) Define amplitude gain and bandwidth as used in an AM transmitter. (2 marks)

(b) Draw a labelled block diagram of a high-level AM transmitter. (6 marks)

(c) An FM modulator has a fixed tuning capacitance of 150 pF in parallel with a 75 pF varactor at a carrier frequency of 80 MHz. Determine the tuned-circuit inductance and the change in varactor capacitance when the frequency is increased to 88 MHz. (6 marks)

(d) A 120 kHz band carries a baseband signal of bandwidth 6 kHz. Determine the number of AM and SSB channels it can accommodate, and state two advantages of VSB over DSB-AM. (6 marks)

QUESTION 6 (20 marks)

(a) Define azimuth angle, apogee and perigee as used in satellite communication. (3 marks)

(b) Draw a labelled block diagram of an earth-station subsystem. (5 marks)

(c) State the approximate frequency ranges of Ku-band and C-band. (4 marks)

(d) An earth station at 12 GHz radiates 5 kW toward a satellite 40,000 km away. The transmitting antenna gain is 50 dB and the received power is 1.2 μW. Determine the wavelength, receiving antenna gain and free-space path loss. (8 marks)

QUESTION 7 (20 marks)

(a) Define monochromaticity, brightness and hue as applied to TV systems. (3 marks)

(b) State one possible cause for each: sound with no video; picture flicker; vertical lines on the screen; and power ON with neither picture nor sound. (4 marks)

(c) A CCTV system has three cameras, a DVR, router and wireless laptop. Draw a labelled block diagram. (7 marks)

(d) A TV standard has 625 lines per frame and 25 frames per second. The screen is 32 inches wide and 18 inches high. Determine line frequency, line period and aspect ratio. (6 marks)

QUESTION 8 (20 marks)

(a) Describe the HLR, VLR and AuC in a GSM cellular network. (6 marks)

(b) With the aid of a labelled diagram, describe the operation of a travelling-wave tube. (8 marks)

(c) A circular waveguide has an internal diameter of 5 cm and operates at 10 GHz in TE_1,1 mode. Using Kc = 1.84, determine cut-off wavelength, guide/group wavelength and TE characteristic impedance. (6 marks)

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End of questions-only mock examination. Submit your attempt for marking or compare it later with the separately stored worked-answer version.