Licensed Electrical Contractor Electrical Theory & Fundamentals 2 — Questions and Answers
Question 1: What happens to the total resistance when resistors are connected in parallel?
- It increases beyond the largest resistor
- It equals the sum of all resistors
- It is always less than the smallest resistor (Correct answer)
- It equals the average of all resistors
Correct answer: It is always less than the smallest resistor
In a parallel circuit, the total resistance is always less than the smallest individual resistor because current has multiple paths.
Question 2: A conductor has a resistance of 10 ohms at 20°C. If the temperature increases, what happens to its resistance?
- Decreases, because heat reduces electron collision
- Increases, because higher temperature increases atomic vibration (Correct answer)
- Remains the same, temperature has no effect
- Decreases to zero at high temperatures
Correct answer: Increases, because higher temperature increases atomic vibration
For most metallic conductors, resistance increases with temperature due to increased atomic vibration impeding electron flow.
Question 3: What is the unit of electrical capacitance?
- Henry
- Ohm
- Farad (Correct answer)
- Weber
Correct answer: Farad
The farad (F) is the SI unit of capacitance, measuring a capacitor's ability to store electric charge.
Question 4: In an AC circuit, what does the term 'reactance' refer to?
- Resistance caused by conductor material
- Opposition to current flow by inductors or capacitors (Correct answer)
- Power dissipated as heat
- Voltage drop across a resistor
Correct answer: Opposition to current flow by inductors or capacitors
Reactance is the opposition to AC current caused by inductance (XL) or capacitance (XC), measured in ohms but unlike resistance it stores rather than dissipates energy.
Question 5: What is the relationship between frequency and inductive reactance (XL)?
- XL decreases as frequency increases
- XL is unaffected by frequency
- XL increases as frequency increases (Correct answer)
- XL equals frequency divided by inductance
Correct answer: XL increases as frequency increases
Inductive reactance XL = 2πfL, so it is directly proportional to frequency — as frequency increases, XL increases.
Question 6: Two 100-ohm resistors are connected in parallel. What is the total resistance?
- 200 ohms
- 100 ohms
- 50 ohms (Correct answer)
- 25 ohms
Correct answer: 50 ohms
For two equal resistors in parallel, total resistance = R/2 = 100/2 = 50 ohms.
Question 7: What is the power factor in a purely resistive AC circuit?
- 0
- 0.5
- 1.0 (Correct answer)
- Varies with voltage
Correct answer: 1.0
In a purely resistive circuit, voltage and current are in phase, so the power factor equals 1.0 (or unity).
Licensed Electrical Contractor Electrical Theory & Fundamentals 2
What happens to the total resistance when resistors are connected in parallel?