Electrical Theory & Principles Flashcards

In a purely inductive AC circuit, the current lags the voltage by how many degrees?

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.

Which law states that the algebraic sum of all currents entering and leaving a node equals zero?

Answer: Kirchhoff's Current Law

Kirchhoff's Current Law (KCL) states that charge conservation requires all currents at a node to sum to zero.

The time constant of an RC circuit is defined as:

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.

What is the equivalent resistance of two 10 Ω resistors connected in parallel?

Answer: 5 Ω

For equal resistors in parallel, the equivalent resistance is R/n = 10/2 = 5 Ω.

Fleming's left-hand rule is used to determine the direction of:

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.

Power factor is defined as the ratio of:

Answer: True power to apparent power

Power factor = True (real) power / Apparent power = cos θ, and ranges from 0 to 1.

Lenz's Law states that an induced current will flow in a direction that:

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.