Alternating Current Mind Map

When a sinusoidal AC voltage is applied across a pure resistor, the current is also sinusoidal and remains in phase with the applied voltage.

Write both instantaneous equations and RMS relation when asked to explain AC through a resistor. Mention phase difference explicitly: phi = 0.

In a pure inductor, current lags voltage by pi/2 and opposition to AC is inductive reactance XL = omega L. In a pure capacitor, current leads voltage by pi/2 and opposition to AC is capacitive reactance XC = 1/(omega C).

For phase questions, mention the leading quantity clearly. For an inductor, voltage leads current by pi/2. For a capacitor, current leads voltage by pi/2.

A series LCR circuit contains a resistor, inductor, and capacitor in series with an AC source; its total opposition to current is impedance Z = sqrt(R^2 + (XL - XC)^2).

Always start the phasor diagram with current as the reference along the horizontal direction because current is common in a series circuit.

Resonance in a series LCR circuit occurs when inductive reactance equals capacitive reactance, making impedance minimum and current maximum.

In resonance questions, immediately write XL = XC, Z = R, phi = 0, and omega0 = 1/sqrt(LC). These four statements cover most scoring points.

Average power consumed in an AC circuit is P = Vrms Irms cos phi, where cos phi is the power factor and phi is the phase difference between voltage and current.

Whenever an AC circuit contains L or C, check the phase angle before calculating average power. Write the power factor clearly.

A transformer is an AC device that changes voltage from one value to another using mutual induction between two coils wound on a common magnetic core.

In transformer numericals, compare turns first. More turns on the secondary means higher secondary voltage; fewer turns means lower secondary voltage.