Module ELTELA1: Semester Test 3 Study Guide

ELTELA1 Semester Test 3 Overview

• Course: Bachelor of Engineering Technology: Electrical

• Module Code: ELTELA1

• Assessment: Semester Test 3

• Date Published/Administered: 16 May 2024

• Total Marks: 40 Marks

• Duration: 80 Minutes

• Examiner: Mr. S.B.K. Ntsaluba

• Total Pages: 8 Pages

Administrative Requirements and Instructions

• Stationery Requirements: Standard stationary and a non-programmable pocket calculator are permitted.

• Submission Rules: All calculations must be included in the script. Answers must be clearly indicated. The script must be submitted at the end of the 80-minute period.

• Writing Material: All working must be completed in pen. Work done in pencil will not be marked.

• Closed Book Policy: This is a closed-book test. No external materials are permitted except writing materials and a calculator.

• Academic Advice: Students are advised to attempt all questions to maximize potential marks.

• Units of Measurement: It is mandatory to indicate correct units for all answers where applicable; failure to include units will result in the loss of marks.

Question 1: Theoretical Principles and AC Fundamentals

• Value: 10 Marks

• Format: True/False Answer Table

• Requirement: The selected answer must hold true under all possible circumstances.

• 1.1: Norton Equilibrium Current Calculation: Determining the Norton equivalent current ($I_N$) requires the load resistor to be replaced with an open circuit.

• 1.2: Thevenin Equivalent Voltage Calculation: Determining the Thevenin equivalent voltage ($V_{TH}$) requires the load resistor to be replaced with a short circuit.

• 1.3: Impedance Equivalence: The statement posits that Thevenin and Norton equivalent impedances are not equal to each other and are therefore not interchangeable.

• 1.4: Resistor-Reactive Definition: The statement suggests the impedance of a capacitor or inductor is purely resistive ($Z = R + jX$, where R > 0 and $X = 0$).

• 1.5: AC Behavior of Components: Under Alternating Current (AC) conditions, a capacitor is replaced with an open circuit and an inductor with a short circuit.

• 1.6: Source Transformation Principles: When considering AC source transformation, a voltage source in series with an impedance is equivalent to a current source in parallel with the same impedance.

• 1.7: Superposition Deactivation Rules: Under AC superposition principles, a voltage source is deactivated by replacing it with an open circuit, while a current source is deactivated by replacing it with a short circuit.

• 1.8: Series Inductor Equivalence: The equivalent impedance of two series-connected inductors is calculated as the arithmetic sum of the individual inductances.

• 1.9: Series Capacitor Impedance: The equivalent impedance of two series-connected capacitors is the arithmetic sum of the individual impedances of the capacitors.

• 1.10: Resistor Stability: Under AC conditions, the value of a resistor remains constant.

Question 2: Sinusoidal Signal Phase Analysis

• Value: 5 Marks

• Given Signal 1 ($V_1$): V_1 = 18\text{cos}(\text{\omega}t + 75^\circ)\,V

• Given Signal 2 ($V_2$): V_2 = 15\text{sin}(\text{\omega}t - 110^\circ)\,V

• Task: Determine the leading/lagging relationship between the two signals.

• Output Requirement: State which signal leads the other and specify the exact phase difference in degrees ($^\circ$).

Question 3: Complex Impedance and Time Domain Equations

• Value: 10 Marks Total

• 3.1: Polar Form Conversion (5 Marks): Calculate the equivalent impedance ($Z_{eq}$) from a provided mathematical expression. The result must be expressed in polar form: $Z_{eq} = \dots \angle \dots ^\circ\,\Omega$.

• 3.2: Time Domain Voltage Equation (5 Marks): Determine the final equation for $V(t)$ in the time domain based on the following input:   - $V(t) = -30\text{sin}(50t) + 30\text{cos}(50t + 50^\circ)\,V$

Question 4: AC Superposition Theorem

• Value: 5 Marks

• Objective: Determine the value of current $I_x$ specifically due to the influence of the current source in the provided circuit.

• Output Requirement: The value of $I_x$ must be provided in polar form ($A \angle \phi$) with units of Amperes ($A$).

Question 5: Circuit component Impedance and Polar Current

• Value: 5 Marks Total

• 5.1: Reactive Impedance (2 Marks): Calculate the specific impedance values for the inductor ($Z_L$) and the capacitor ($Z_C$) based on the circuit diagram.

• 5.2: Polar Current Determination (3 Marks): Calculate the total current ($i$) for the circuit and express it in polar form: $i = \dots \angle \dots ^\circ\,\Omega$ (Note: The prompt in the transcript indicates units of $\Omega$, implying an impedance calculation or a typo in the original transcript intended for current in Amperes).

Question 6: Thevenin Equivalent Parameters

• Value: 5 Marks Total

• 6.1: Thevenin Impedance (2 Marks): Determine the Thevenin equivalent impedance ($Z_{TH}$) with respect to the specific terminals labelled ab in the circuit. The final value must be in polar form ($\Omega$, deg).

• 6.2: Thevenin Voltage (3 Marks): Determine the Thevenin equivalent voltage ($V_{TH}$) with respect to terminals ab. The final value must be in polar form ($V \angle \phi$).

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