Alternating Current Practice Flashcards

These flashcards cover the fundamental principles of Alternating Current, including components (resistors, inductors, capacitors), LCR circuits, resonance, power factors, and transformers.

Alternating voltage (ac voltage)

A voltage that varies like a sine function with time, commonly supplied by electric mains in homes and offices.

Alternating current (ac current)

The current driven in a circuit by an alternating voltage, characterized by simple harmonic time dependence.

Nicola Tesla

A Serbian-American scientist and inventor who conceived the rotating magnetic field and invented the induction motor, the polyphase ac power system, and the Tesla coil.

Inductive Reactance ($X_L$)

A quantity analogous to resistance that limits current in a purely inductive circuit, defined as $X_L = \text{ω} L$, and measured in $\text{ohm (Ω)}$.

Capacitive Reactance ($X_C$)

An impedance-like quantity that limits the current in a purely capacitive circuit, defined as $X_C = \frac{1}{\text{ω} C}$, and measured in $\text{ohm (Ω)}$.

Root Mean Square (rms) Current ($I$)

The effective current value equivalent to the direct current that would produce the same average power loss; it is related to peak current by $I = \frac{i_m}{\text{√} 2} \text{≈} 0.707 i_{m}$.

Root Mean Square (rms) Voltage ($V$)

The effective voltage value, given by $V = \frac{v_m}{\text{√} 2} \text{≈} 0.707 v_{m}$, used as the standard measurement for ac quantities like household supply.

Phasor

A scalar quantity represented by a rotating vector that rotates about the origin with angular speed $\text{ω}$, where the vertical component represents the sinusoidally varying quantity.

Impedance ($Z$)

The total effective resistance to current flow in an ac circuit, given for a series LCR circuit by $Z = \text{√}(R^2 + (X_C - X_L)^2)$.

Resonance

A phenomenon in a series RLC circuit where the current amplitude is maximum because the resonant frequency $\text{ω}_0 = \frac{1}{\text{√} LC}$ makes $X_C = X_L$.

Power Factor

The term $\text{cos}(\text{φ})$ representing the cosine of the phase angle between voltage and current, which determines the average power dissipated in an ac circuit.

Wattless Current

The current flowing in a purely inductive or capacitive circuit where the phase difference is $\text{π}/2$, resulting in zero power dissipation despite current flow.

Transformer

A device used to increase or decrease alternating voltage based on the principle of mutual induction between a primary and a secondary coil wound on a soft-iron core.

Step-up Transformer

A transformer where the secondary coil has more turns than the primary coil ($N_s > N_p$), resulting in a higher output voltage and lower current.

Step-down Transformer

A transformer where the secondary coil has fewer turns than the primary coil ($N_s < N_p$), resulting in a lower output voltage and higher current.

Eddy Currents

Currents induced in the iron core of a transformer by alternating magnetic flux that cause heating losses; these are reduced by using a laminated core.

Hysteresis

A source of energy loss in transformer cores caused by the repeated reversal of magnetization, minimized by using materials with low hysteresis loss.

George Westinghouse

A leading proponent of ac technology who founded a major company and enlisted Nicola Tesla to develop ac motors and high tension current transmission.