Basic Electrical Engineering Interview Questions 3

• What is Voltage Divider Rule?

Voltage divider rule provides a useful formula to determine the voltage across any resistor when two or more resistors are connected in series with a voltage source.

• What is Kirchoff ’s Current Law (KCL)?

The algebraic sum of all the currents entering or leaving a node in an electric circuit is
equal to zero. In other words, the sum of currents entering is equal to the sum of currents leaving the node in an electric circuit.

• What is Current Divider Rule (CDR)?

Current divider rule provides a useful relationship for determining the current through individual circuit elements that are connected in parallel.

• What is Superposition Theorem?

Superposition theorem is extremely useful for analyzing electric circuits that contains two or more active sources. In such cases, the theorem considers each source separately to evaluate the current through or voltage across a component. The resultant is given by the algebraic sum of all currents or voltages caused by each source acting independently. Superposition theorem can be formally stated
as follows:

“The current through or voltage across any element in a linear circuit containing several sources is the algebraic sum of the currents or voltages due to each source acting alone, all other sources being removed at that time.”

• Please elaborate Th´evenin’s Theorem?

Th´evenin’s theorem provides a useful tool when solving complex and large electric circuits by reducing them to a single voltage source in series with a resistor. It is particularly advantageous where a single resistor or load in a circuit is subject to change. Formally, the Th´evenin’s theorem can be stated as:

“Any two-terminal linear electric circuit consisting of resistors and sources, can be re-placed by an equivalent circuit containing a single voltage source in series with a resistor connected across the load.”
he following steps outline the procedure to simplify an electric circuit using Th´evenin’s theorem
where VTH and RTH are the Th´evenin’s voltage and Th´evenin’s resistance respectively.
1. Remove the load resistance RL.
2. VTH is the open circuit (OC) voltage across the load terminals and
3. RTH is the resistance across the load terminals with all sources replaced by their internal resistances.

• State and define Norton’s Theorem?

Th´evenin’s equivalent circuit is a practical voltage source. In contrast, Norton’s equivalent circuit is a practical current source. This can be formally stated as:

“Any two-terminal, linear circuit, of resistors and sources, can be replaced by a single
current source in parallel with a resistor.”

To determine Norton’s equivalent circuit, Norton current, IN , and Norton resistance, RN , are required. The following steps outline the procedure required:

1. Remove the load resistance, RL.
2. IN is the SC current through the load terminals and
3. RN is the resistance across the load terminals with all sources replaced by their internal resistances. Clearly RN = RTH .

• What is the method to solve circuit using Source Transformation?

In an electric circuit, it is often convenient to have a voltage source rather than a current source (e.g. in mesh analysis) or vice versa. This is made possible using source transformations. It should be noted that only practical voltage and current sources can be transformed. In other words, a Th´evenin’s equivalent circuit is transformed into a Norton’s one or vice versa. The parameters used in the source
transformation are given as follows.
Th´evenin parameters: VTH ,RTH =⇒ RN = RTH ,IN = VTH/RTH
Norton parameters: IN ,RN =⇒ RTH = RN ,VTH = RN IN
Any load resistance, RL will have the same voltage across, and current through it when connected across the terminals of either source.