Electrical Theory and Principles Flashcards
7 cards from real IEC practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Electrical Theory and Principles flashcards as text
What is the phase relationship between voltage and current in a purely inductive circuit?
Answer: Current lags voltage by 90°
In a purely inductive circuit, current lags voltage by 90° because the inductor opposes changes in current.
A transformer has 500 turns on the primary and 100 turns on the secondary. If the primary voltage is 240V, what is the secondary voltage?
Answer: 48V
Using the turns ratio formula: Vs = Vp × (Ns/Np) = 240 × (100/500) = 48V.
Which of the following best describes impedance in an AC circuit?
Answer: The total opposition to AC current flow including resistance and reactance
Impedance (Z) is the total opposition to AC current and is the vector sum of resistance and reactance.
What happens to capacitive reactance as frequency increases?
Answer: It decreases
Capacitive reactance (Xc = 1/2πfC) is inversely proportional to frequency, so it decreases as frequency increases.
In a series RLC circuit at resonance, which statement is true?
Answer: Inductive and capacitive reactances are equal and cancel
At resonance, XL = XC, they cancel each other, and the circuit impedance equals only the resistance.
What is the unit of magnetic flux?
Answer: Weber
The Weber (Wb) is the SI unit of magnetic flux, where 1 Wb = 1 V·s.
According to Faraday's Law, EMF is induced in a conductor when:
Answer: The magnetic flux through it changes
Faraday's Law states that induced EMF is proportional to the rate of change of magnetic flux through the conductor.