Lineman Electrical Theory and Principles 2 โ Questions and Answers
Question 1: A single-phase transformer has a primary voltage of 7,200V and a secondary voltage of 240V. What is the turns ratio?
- 10:1
- 20:1
- 30:1 (Correct answer)
- 40:1
Correct answer: 30:1
Turns ratio = primary voltage รท secondary voltage = 7,200V รท 240V = 30:1.
Question 2: What formula is used to calculate electrical power in a DC circuit?
- P = V / I
- P = V ร R
- P = V ร I (Correct answer)
- P = I / V
Correct answer: P = V ร I
Power (P) in watts equals voltage (V) multiplied by current (I), expressed as P = V ร I.
Question 3: Inductive reactance (XL) in an AC circuit increases as frequency:
- Decreases
- Increases (Correct answer)
- Remains constant
- Reaches resonance
Correct answer: Increases
Inductive reactance XL = 2ฯfL, so it increases proportionally with frequency; higher frequency means greater opposition to current from an inductor.
Question 4: What is the RMS (root mean square) voltage of a standard US 120V AC outlet in relation to its peak voltage?
- Peak voltage equals RMS voltage
- Peak voltage is approximately 1.414 times the RMS voltage (Correct answer)
- Peak voltage is exactly twice the RMS voltage
- RMS voltage is 1.732 times the peak voltage
Correct answer: Peak voltage is approximately 1.414 times the RMS voltage
For a sinusoidal waveform, peak voltage = RMS ร โ2 โ 1.414 ร RMS, so a 120V RMS outlet has a peak of about 170V.
Question 5: Kirchhoff's Current Law (KCL) states that at any node in a circuit:
- Voltage is equal at all branches
- The sum of all currents entering equals the sum of all currents leaving (Correct answer)
- Total resistance equals total reactance
- Power dissipated equals power supplied to each branch
Correct answer: The sum of all currents entering equals the sum of all currents leaving
KCL is based on conservation of charge: the total current entering a junction must equal the total current leaving it.
Question 6: Which type of power is measured in volt-amperes reactive (VAR)?
- True power
- Apparent power
- Reactive power (Correct answer)
- Real power
Correct answer: Reactive power
Reactive power, measured in VARs, represents energy stored and released by inductors and capacitors and does no useful work.
Question 7: A conductor carrying 200 amps over a resistance of 0.05 ohms will dissipate how much power as heat?
- 500 watts
- 1,000 watts
- 2,000 watts (Correct answer)
- 4,000 watts
Correct answer: 2,000 watts
Using P = IยฒR: (200)ยฒ ร 0.05 = 40,000 ร 0.05 = 2,000 watts of heat dissipated.
Lineman Electrical Theory and Principles 2
A single-phase transformer has a primary voltage of 7,200V and a secondary voltage of 240V.
What is the turns ratio?