Electrical and Electronic Theory Flashcards

A technician is analyzing a DC series circuit containing three resistors: R1 = 10 Ω, R2 = 20 Ω, and R3 = 30 Ω, connected to a 120 V source. What is the total current flowing through the circuit?

Answer: 2.0 A

In a series circuit, the total resistance (Rt) is the sum of the individual resistances. Rt = R1 + R2 + R3 = 10 Ω + 20 Ω + 30 Ω = 60 Ω. According to Ohm's Law (V = IR), the total current (I) is the total voltage (V) divided by the total resistance (Rt). I = 120 V / 60 Ω = 2.0 A.

Which of the following statements is a fundamental characteristic of a parallel circuit?

Answer: The voltage across each component is the same.

In a parallel circuit, components are connected across the same two points, meaning the voltage potential difference across each parallel branch is identical and equal to the source voltage. Current divides among the branches, and total resistance is calculated by the reciprocal formula, always resulting in a value less than the smallest individual resistor.

An uncharged capacitor is connected to a DC power source. What is the initial behavior of the current when the circuit is first energized?

Answer: The current is at its maximum and then decays to zero.

When first connected to a DC source, an uncharged capacitor acts like a short circuit, allowing the maximum possible current (limited only by circuit resistance) to flow. As the capacitor's plates accumulate charge, a voltage builds up across it, opposing the source voltage. This causes the current to exponentially decay to zero once the capacitor is fully charged.

An inductor is placed in a circuit where the current is increasing. According to Lenz's Law, the inductor will generate a voltage (back EMF) that:

Answer: opposes the increase in current.

Lenz's Law, a consequence of the conservation of energy, states that the induced electromotive force (EMF) in an inductor will create a current whose magnetic field opposes the change in magnetic flux that produced it. Therefore, if the current is increasing, the inductor's back EMF will oppose that increase.

At a junction (or node) in an electrical circuit, two currents of 3 A and 5 A are flowing into the node. If one current of 2 A is flowing out of the node, what must be the value and direction of the fourth current according to Kirchhoff's Current Law (KCL)?

Answer: 6 A, flowing out

Kirchhoff's Current Law (KCL) states that the algebraic sum of currents entering a node must equal the sum of currents leaving the node. Total current in: 3 A + 5 A = 8 A. Total current out must also be 8 A. Since 2 A is already leaving, the fourth current must be 8 A - 2 A = 6 A, flowing out of the node.

What is the primary difference between Alternating Current (AC) and Direct Current (DC)?

Answer: AC periodically reverses its direction of flow, while DC flows in only one direction.

The fundamental distinction between AC and DC is the direction of electron flow. In Direct Current (DC), the electric charge flows consistently in one direction. In Alternating Current (AC), the flow of electric charge periodically reverses direction.