Lineman Electrical Theory and Principles 2

Question 1

A single-phase transformer has a primary voltage of 7,200V and a secondary voltage of 240V. What is the turns ratio?

Accepted Answer

30:1

Answer

Turns ratio = primary voltage ÷ secondary voltage = 7,200V ÷ 240V = 30:1.

Question 2

What formula is used to calculate electrical power in a DC circuit?

Accepted Answer

P = V × I

Answer

Power (P) in watts equals voltage (V) multiplied by current (I), expressed as P = V × I.

Question 3

Inductive reactance (XL) in an AC circuit increases as frequency:

Accepted Answer

Increases

Answer

Inductive reactance XL = 2πfL, 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?

Accepted Answer

Peak voltage is approximately 1.414 times the RMS voltage

Answer

For a sinusoidal waveform, peak voltage = RMS × √2 ≈ 1.414 × 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:

Accepted Answer

The sum of all currents entering equals the sum of all currents leaving

Answer

KCL is based on conservation of charge: the total current entering a junction must equal the total current leaving it.

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