CEP Electrical Theory & Principles 2 — Questions and Answers
Question 1: In a purely inductive AC circuit, the current lags the voltage by how many degrees?
- 45 degrees
- 90 degrees (Correct answer)
- 180 degrees
- 0 degrees
Correct answer: 90 degrees
In a purely inductive circuit, current lags voltage by exactly 90 degrees due to the inductor's opposition to changes in current.
Question 2: Which law states that the algebraic sum of all currents entering and leaving a node equals zero?
- Faraday's Law
- Kirchhoff's Voltage Law
- Kirchhoff's Current Law (Correct answer)
- Ohm's Law
Correct answer: Kirchhoff's Current Law
Kirchhoff's Current Law (KCL) states that charge conservation requires all currents at a node to sum to zero.
Question 3: The time constant of an RC circuit is defined as:
- R × C (Correct answer)
- R / C
- 1 / (R × C)
- √(R × C)
Correct answer: R × C
The RC time constant τ = R × C represents the time for the capacitor to charge to approximately 63.2% of the supply voltage.
Question 4: What is the equivalent resistance of two 10 Ω resistors connected in parallel?
- 20 Ω
- 10 Ω
- 5 Ω (Correct answer)
- 2.5 Ω
Correct answer: 5 Ω
For equal resistors in parallel, the equivalent resistance is R/n = 10/2 = 5 Ω.
Question 5: Fleming's left-hand rule is used to determine the direction of:
- Induced EMF in a generator
- Force on a current-carrying conductor in a magnetic field (Correct answer)
- Magnetic flux around a solenoid
- Current flow in a transformer
Correct answer: Force on a current-carrying conductor in a magnetic field
Fleming's left-hand rule relates the directions of magnetic field, current, and mechanical force on a motor conductor.
Question 6: Power factor is defined as the ratio of:
- Apparent power to reactive power
- True power to apparent power (Correct answer)
- Reactive power to true power
- Apparent power to true power
Correct answer: True power to apparent power
Power factor = True (real) power / Apparent power = cos θ, and ranges from 0 to 1.
Question 7: Lenz's Law states that an induced current will flow in a direction that:
- Amplifies the change in magnetic flux
- Has no relationship to the change in flux
- Opposes the change in magnetic flux that caused it (Correct answer)
- Doubles the applied voltage
Correct answer: Opposes the change in magnetic flux that caused it
Lenz's Law is a consequence of conservation of energy, ensuring induced currents oppose the flux change producing them.
CEP Electrical Theory & Principles 2
In a purely inductive AC circuit, the current lags the voltage by how many degrees?