BEE Bachelor of Electrical Engineering Fundamental Circuit Analysis Questions and Answers — Questions and Answers
Question 1: According to Kirchhoff's Current Law (KCL), what is the fundamental principle governing the flow of current at any node (junction) in an electrical circuit?
- The algebraic sum of currents entering and leaving the node is zero. (Correct answer)
- The total voltage at the node must be equal to the source voltage.
- The current leaving the node is always greater than the current entering it.
- The algebraic sum of resistances connected to the node is constant.
Correct answer: The algebraic sum of currents entering and leaving the node is zero.
Kirchhoff's Current Law is based on the principle of conservation of charge. It states that because charge cannot accumulate at a node, the total amount of current flowing into a node must be equal to the total amount of current flowing out of it. Therefore, the algebraic sum of all currents entering and leaving the node must be zero.
Question 2: In a DC circuit, a 10V source is connected to a series combination of a 3Ω resistor and a 2Ω resistor. What is the power dissipated by the 3Ω resistor?
- 18 W
- 12 W (Correct answer)
- 30 W
- 50 W
Correct answer: 12 W
First, calculate the total resistance (Req) of the series circuit: Req = R1 + R2 = 3Ω + 2Ω = 5Ω. Next, use Ohm's Law to find the total current (I) flowing through the circuit: I = V / Req = 10V / 5Ω = 2A. Since the resistors are in series, the same current flows through both. Finally, calculate the power (P) dissipated by the 3Ω resistor using the formula P = I²R: P = (2A)² * 3Ω = 4 * 3 = 12 W.
Question 3: Which of the following statements is true regarding a capacitor in a DC circuit after it has been fully charged?
- It acts as a short circuit.
- It continuously draws maximum current from the source.
- It acts as an open circuit. (Correct answer)
- Its voltage is zero.
Correct answer: It acts as an open circuit.
When a capacitor is connected to a DC source, it charges up. Once fully charged, the voltage across the capacitor equals the source voltage. At this point, the capacitor opposes any further flow of DC current, effectively behaving like an open circuit. No more current flows through the capacitor branch.
Question 4: A circuit designer needs to find a simplified equivalent circuit for a complex linear network. The equivalent circuit should consist of a single voltage source and a single series resistor. Which theorem should be applied?
- Norton's Theorem
- Superposition Theorem
- Maximum Power Transfer Theorem
- Thevenin's Theorem (Correct answer)
Correct answer: Thevenin's Theorem
Thevenin's theorem states that any two-terminal linear electrical network can be replaced by an equivalent circuit composed of a single voltage source (Vth) in series with a single resistor (Rth). This is precisely what the scenario describes.
Question 5: For maximum power to be transferred from a DC voltage source with an internal resistance (Rs) to a connected load resistance (RL), what must be the relationship between the resistances?
- RL must be significantly larger than Rs.
- RL must be equal to Rs. (Correct answer)
- RL must be significantly smaller than Rs.
- RL must be twice the value of Rs.
Correct answer: RL must be equal to Rs.
The Maximum Power Transfer Theorem states that for a DC circuit, the maximum power is delivered to the load resistor (RL) when the load resistance is equal to the Thevenin equivalent resistance of the source (Rth), which in this case is the internal resistance (Rs).
Question 6: In an AC circuit containing only a pure inductor, what is the phase relationship between the voltage across the inductor and the current flowing through it?
- The voltage and current are in phase.
- The current lags the voltage by 90 degrees.
- The voltage lags the current by 90 degrees. (Correct answer)
- The voltage and current are 180 degrees out of phase.
Correct answer: The voltage lags the current by 90 degrees.
In a purely inductive AC circuit, the voltage across the inductor leads the current flowing through it by 90 degrees. Conversely, the current lags the voltage by 90 degrees. This is because the voltage across an inductor is proportional to the rate of change of the current (v = L * di/dt).
BEE Bachelor of Electrical Engineering Fundamental Circuit Analysis Questions and Answers
According to Kirchhoff's Current Law (KCL), what is the fundamental principle governing the flow of current at any node (junction) in an electrical circuit?