EEE Central Viva Prep

eee-1109 EEE-1109 Basic Electrical Engineering

lab experiments summarised

2. Verification of Ohm’s Law, KCL, and KVL (Exp 02)

Experiment	Process Description	Key Formulae
Ohm’s Law	A simple series circuit containing a resistor ($R$) and an ammeter was connected to a DC source ($V_S$). The source voltage ($V_S$) was varied from $2\text{ V}$ to $20\text{ V}$, and the corresponding current ($I$) was measured. A graph of Current ($I$) vs. Voltage ($V$) was plotted to verify the linear relationship.	Ohm’s Law: $V=I\times R$ or $R=\frac{\Delta V}{\Delta I}$ (from graph slope). Percentage Error $= \left
KVL Verification	A series DC circuit with two resistors ($R_1,R_2$) was constructed. The source voltage ($V_S$) was varied, and the current ($I_S$) was measured. The voltage drops across $R_1$ ($V_1$) and $R_2$ ($V_2$) were measured for each $V_S$ value.	KVL Verification: $\sum V=0$ or $\sum V_i=V_{\text{Total}}$ (Source voltage should equal the sum of drops: $V_S\approx V_1+V_2$).
KCL Verification	A parallel DC circuit with two resistors ($R_1,R_2$) was constructed. Ammeters were used to measure the total source current ($I_S$) and the current in each parallel branch ($I_1,I_2$). Measurements were recorded for various source voltages.	KCL Verification: $\sum I=0$ or $\sum I_{\text{incoming}}=\sum I_{\text{outgoing}}$ (Source current should equal the sum of branch currents: $I_S\approx I_1+I_2$).

3. Verification of Superposition Theorem (Exp 03)

Experiment	Process Description	Key Formulae
Superposition Theorem	This experiment verified the theorem in a circuit with two DC voltage sources ($E_1,E_2$) and three resistors ($R_1,R_2,R_3$) in a bridge-like configuration. Step 1: Measured branch currents ($I_1,I_2,I_3$) with both sources active. Step 2: Measured current components ($I^{\prime },I_2^{\prime },I_3^{\prime }$) with $E_1$ active (and $E_2$ shorted). Step 3: Measured current components ($I_1^{\prime \prime },I_2^{\prime \prime },I_3^{\prime \prime }$) with $E_2$ active (and $E_1$ shorted).	Superposition Verification: Total current in any branch is the algebraic sum of the individual component currents: $I_{\text{Total}}=I_{\text{Source 1}}+I_{\text{Source 2}}$ (e.g., $I_1=I_1^{\prime }+I_1^{\prime \prime }$).

4. Series and Parallel RL Circuits (Exp 05, related to Exp 10)

Experiment	Process Description	Key Formulae
RL Circuit Analysis	Constructed series and parallel AC circuits consisting of a resistor ($R$, represented by a bulb) and an inductor ($L$, represented by a ballast). The experiment determined the resistance, reactance, and total impedance of the circuit, and plotted the voltage/current relationship using a phasor diagram.	Inductive Reactance: $X_L=2\pi fL$.

5. Series RLC Circuit (Exp 06)

Experiment	Process Description	Key Formulae
RLC Circuit Impedance	Constructed a series RLC circuit (Resistor/Bulb, Inductor/Ballast, Capacitor) connected to an AC source. Measured the voltage drops across each component and the total circuit current to calculate the resistance ($R$), reactance ($X_L,X_C$), and impedance ($Z$).	Capacitive Reactance: $X_C=\frac{1}{2\pi fC}$. Inductive Reactance: $X_L = \sqrt{

6. Three-Phase Circuits (Y and $\Delta$) (Exp 07)

Experiment	Process Description	Key Formulae
Y and $\Delta$ Characteristics	Two three-phase circuits were constructed using three identical loads (bulbs) connected first in a Wye (Y) configuration, and then in a Delta ($\Delta$) configuration. Ammeters and Voltmeters were used to measure phase voltages ($V_P$), line voltages ($V_L$), phase currents ($I_P$), and line currents ($I_L$) for both connections.	Wye Connection: $V_L=\sqrt{3}{V}_P$ and $I_L=I_P$. Delta Connection: $V_L=V_P$ and $I_L=\sqrt{3}{I}_P$.

Laws and Theorems

Concept	Definition
Ohm’s Law	States that the voltage across a conductor is directly proportional to the current flowing through it, for any given temperature, expressed as $E=I\times R$ or $V=IR$.
Kirchhoff’s Current Law (KCL)	The algebraic sum of all the currents at any node point or junction of a circuit is zero. Equivalently, the sum of incoming currents equals the sum of outgoing currents.
Kirchhoff’s Voltage Law (KVL)	The algebraic sum of the voltages (or voltage drops) in any closed path of a network that is traversed in a single direction is zero.
Superposition Theorem	States that a circuit with multiple voltage and current sources is equal to the sum of simplified circuits using just one of the sources at a time. The individual voltages and currents are then “superimposed” (algebraically summed) to find the actual values.

Components

Component	Definition/Function
Resistor	A passive electrical component that creates resistance in the flow of electric current.
Capacitor	A passive electronic device consisting of two or more pieces of conducting material separated by an insulating material (dielectric). It has the ability to store energy in the form of electrical charge (static voltage).
Inductor (Coil)	A passive two-terminal component that temporarily stores energy in the form of a magnetic field. It fundamentally opposes any change in the current.

AC and Three-Phase Circuit Concepts

Concept	Definition
Impedance ($Z$)	The total opposition to the current flow in an AC circuit, taking into account both resistance and reactance.
Reactance ($X_L$ or $X_C$)	The opposition to current flow offered specifically by an inductor ($X_L$) or a capacitor ($X_C$) in an AC circuit.
Phasor Diagram	A graphical tool used to represent the AC voltage and current waveforms to visualize the phase relationship between the properties of the circuit elements used.
Resonance (RLC)	In an RLC circuit, at the resonant frequency, the reactance of the inductor and capacitor cancel out, resulting in a minimum impedance and maximum current flow.
Three-Phase Circuit	An electrical system consisting of three conductors carrying alternating current, offset by $120^{\circ }$ from each other. Power is delivered in a more uniform and balanced way compared to single-phase.
Two Wattmeter Method	A widely used technique for three-phase power measurement that employs two wattmeters to measure the power in two of the three phases. The sum of the readings gives the total power consumed.
Phase Sequence	Refers to the order in which the voltages of the three phases change over time. A positive sequence indicates the order A-B-C.
Wye (Y) Connection	A three-phase connection where the line current is equal to the phase current ($I_L=I_P$), and the line voltage is $\sqrt{3}$ times the phase voltage ($V_L=\sqrt{3}{V}_P$).
Delta ($\Delta$) Connection	A three-phase connection where the line voltage is equal to the phase voltage ($V_L=V_P$), and the line current is $\sqrt{3}$ times the phase current ($I_L=\sqrt{3}{I}_P$).

Connection Methods

Instrument / Component	Primary Function	Principle of Connection / Usage
Ammeter	Used to measure the current ($I$) in a circuit.	For direct measurement, the ammeter is connected in series with the circuit or component where the current is to be measured. It is designed to have low resistance to avoid causing a significant voltage drop.
Wattmeter	Used to measure electric power given to or developed by a circuit.	Consists of two main coils: 1. Current Coil (fixed): Connected in series with the load. 2. Potential Coil (moving): Connected across the load (in parallel) through a series multiplier resistance.
Analog Multimeter	A versatile measuring instrument that can measure multiple electrical properties, including voltage, current, and resistance.	Used by switching to the appropriate range. Used in the lab to measure the resistance of elements like Zener diodes and fixed resistors. Also used for precise measurements in experiments like the Superposition Theorem verification.