ECE Viva Study Guide

ece-1109 ECE-1109 Introduction to ECE

This comprehensive note expands the previous response into a detailed, question-based table, providing enhanced preparation for your viva by drawing extensively on the core concepts and definitions present in the source material.

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I. Fundamentals and Component Familiarization (Ohm’s Law)

Concept	Question	Answer/Explanation
Current Definition	Define the unit of electrical current, the ampere, in terms of electron flow.	The ampere is the unit of electrical current, defined as one coulomb (which is $6.28\times 10^{18}$ electrons) passing any given point in a conductor in one second.
Ohm’s Law Statement	How does current relate to voltage and resistance according to Ohm’s Law?	Current ($I$) is directly proportional to the voltage (E) and inversely proportional to the resistance (R). This can be written as $I=E/R$.
Voltage Polarity/Term Definition	What is the voltage?	The voltage is the electrical pressure, EMF, or potential difference that exists between two points in a circuit.

II. Verifying KCL/KVL & Series-Parallel Circuits

Concept	Question	Answer/Explanation
Kirchhoff’s Current Law (KCL)	Provide both ways of stating Kirchhoff’s Current Law.	1. The sum of the currents leaving a circuit junction is equal to the sum of the currents entering the junction. 2. The algebraic sum of the currents at any junction in a circuit is zero.
Parallel Circuit Voltage Rule	Why does removing one parallel branch in a circuit, while keeping the source voltage fixed, not change the current flow in the other remaining branches?	Because the voltage remains the same across each branch in a parallel circuit.
Voltage Dividers (Loading)	How does connecting an external load resistance to a voltage divider typically affect the total current and the output voltage distribution?	Connecting a load draws current from the divider, causing the input current and voltage distribution of the divider to change. A higher value load resistance causes less loading effect and smaller changes in the circuit values.

III. Thevenin’s and Norton’s Theorems

Concept	Question	Answer/Explanation	Source(s)
Thevenin’s Theorem	Define the equivalent circuit derived using Thevenin’s Theorem.	Any complex circuit between two terminals can be replaced with a single equivalent series circuit consisting of a Thevenin voltage ($V_{TH}$) in series with a Thevenin resistance ($R_{TH}$).
Calculating $V_{TH}$	How is the equivalent Thevenin voltage ($V_{TH}$) determined in the original circuit?	$V_{TH}$ is the open-circuit voltage measured across the load resistance terminals (A and B) of the original circuit.
Calculating $R_{TH}$	How is the Thevenin resistance ($R_{TH}$) determined?	$R_{TH}$ is the resistance seen between the two internal terminals (A and B) of the original circuit when the internal voltage sources are assumed to be zero (short-circuited).
Norton’s Theorem Equivalent	Define the equivalent circuit derived using Norton’s Theorem.	Any complex circuit between two terminals can be replaced with a single equivalent parallel circuit consisting of a Norton current source ($I_N$) in parallel with a Norton resistance ($R_N$).
Thevenin-Norton Relationship	How are the Thevenin equivalent values ($V_{TH}$ and $R_{TH}$) mathematically related to the Norton equivalent values ($I_N$ and $R_N$)?	The Thevenin resistance is equal to the Norton resistance ($R_N=R_{TH}$). The voltage and current are related by $V_{TH}=I_N\times R_{TH}$ or $I_N=V_{TH}/R_{TH}$.

IV. AC and DC Measurement

Concept	Question	Answer/Explanation
DC Voltmeter Design	What component is placed in series with the basic meter movement to create a DC voltmeter, and why is high input resistance desired?	A voltage multiplier resistor is placed in series. The input resistance must be very high compared to the circuit being measured to prevent loading the circuit.
Voltmeter Sensitivity	What does the voltage sensitivity specification of a voltmeter indicate?	Voltage sensitivity is given in ohms-per-volt. It relates the input resistance and current requirements, which indicate the amount of loading the meter has on the circuit being measured.
DC Ammeter Design	How is the range of a DC ammeter extended, and why should its resistance be very low?	The range is extended by adding a shunt resistor (parallel resistance) across the meter movement. The resistance of a good ammeter should be very low, preferably zero, so as not to reduce the true current flow in the series circuit.
Ohmmeter Principle	How does an ohmmeter measure resistance, and what is the role of the rheostat?	An ohmmeter measures resistance indirectly by measuring the current flow through a series circuit composed of an internal voltage source, the meter movement, and the unknown resistor. A rheostat (variable resistor) is usually used to compensate for variations in the internal meter supply voltage, serving as the “zero adjust” control.

V. Diode Characteristics and Half Wave Rectification

Concept	Question	Answer/Explanation
Diode Definition/Function	What is the fundamental function of a PN junction diode?	A diode is a semiconductor device that permits current to flow through it in one direction only.
Forward Bias Resistance	What resistance state does a diode exhibit when it is forward biased?	It exhibits low forward resistance. A good silicon diode should measure between $50\Omega$ to $300\Omega$ in forward bias.
Reverse Bias Resistance	What resistance state does a diode exhibit when it is reverse biased, and what is the expected ratio of resistance?	It exhibits very high reverse resistance. Good silicon diodes should measure between $10\text{M}\Omega$ to $100\text{M}\Omega$ in reverse bias. The ratio of reverse resistance to forward resistance determines the quality of the diode, typically being much greater than 10,000 to 1.
Forward Voltage Drop	What is the typical forward voltage drop across a fully conducting silicon diode?	The typical forward voltage drop is approximately 0.5 to 0.7 volts for a silicon diode.
Reverse Current	What happens to the reverse leakage current if the reverse voltage is increased?	When the reverse voltage is increased, the reverse leakage current ($I_R$) usually remains very small and relatively constant until the breakdown voltage is reached, at which point the current increases very rapidly.

(Note: The sources do not contain relevant information for verifying truth tables of logic gates, AC measurements using an oscilloscope, or specific rectifier circuits like counter-tapped and bridge full-wave rectification beyond the basic diode characteristics.)

VI. BJT Transistors (Structure, Biasing, Testing, and Stabilization)

Concept	Question	Answer/Explanation	Source(s)
Transistor Regions	What are the three regions of a bipolar transistor, and what determines if it is NPN or PNP?	The three regions are the base, emitter, and collector. Bipolar transistors are either NPN or PNP type semiconductors.
Amplifier Operation Biasing	For a transistor to operate normally as an amplifier, what bias must be applied to the base-emitter and collector-base junctions?	The base-emitter junction must be forward biased, and the collector-base junction must be reverse biased.
Current Control	What is the fundamental relationship between the three terminal currents, and what makes the BJT a current controlling device?	Emitter current ($I_E$) is the sum of the base and collector currents ($I_E=I_B+I_C$). A BJT is a current controlling device because a small change in base current ($I_B$) can cause a large change in collector current ($I_C$), providing amplification.
Transistor Testing (Ohmeter)	When checking a transistor using an ohmmeter, how does the forward resistance of the base-emitter junction compare to the reverse resistance?	Typical forward resistance is very low (less than $20\Omega$ to $200\Omega$), while the reverse resistance is very high (from $10\text{k}\Omega$ to $100\text{M}\Omega$).
Bias Stabilization	What is the major environmental factor that creates instability in transistors, and what specific current is affected?	Temperature changes have an adverse effect. Increased temperature causes a rise in collector leakage current ($I_{CBO}$), which further increases collector current, leading to thermal runaway (instability).
Silicon vs. Germanium	How does leakage current compare between silicon and germanium transistors, and how does leakage current change with temperature for each?	Silicon transistors have less leakage current than germanium transistors. Leakage current ($I_{CBO}$) approximately doubles for every $10^{\circ }C$ increase in temperature for germanium, but only doubles for every $6^{\circ }C$ increase for silicon.

VII. Transistor Specification Sheet (Characteristics)

Concept	Question	Answer/Explanation	Source(s)
Maximum Ratings	What are “Maximum Ratings,” and why is operating a transistor near them unacceptable?	Maximum ratings are the absolute limits for voltage, current, power dissipation, and temperature that the transistor can withstand without permanent damage or degradation. A transistor should never be operated at or near its maximum ratings.
Characteristic Curves	What are Characteristic Curves used for?	These are graphic plots showing how transistor parameters vary with changes in temperature, voltage, current, etc. They are used to further define the electrical characteristics and aid the user in selecting the correct transistor for a specific application.
Common Abbreviations	What does the symbol $V_{CEO}$ represent, and what does $I_C$ represent?	$V_{CEO}$ represents Collector-to-Emitter Breakdown Voltage, with the base open. $I_C$ represents Collector Current (instantaneous or DC).
Small Signal Characteristics	If you are selecting a transistor for an amplifier, which categories of information on the spec sheet are most relevant?	Electrical Characteristics, including small-signal characteristics (like current gain, input impedance, etc.), are typically important for amplifier design.