Intermediate
AC Fundamentals
Sinusoidal voltage, RMS values and power factor.
STEP 1 · CONCEPT
AC voltage varies sinusoidally. In India the supply is 230 V RMS at 50 Hz.
STEP 2 · RMS
The RMS value gives the same heating effect as an equal DC value.
STEP 3 · POWER FACTOR
cos φ tells how much of the current does useful work. Motors often have lagging power factor.
WORKED EXAMPLE
Peak voltage of 230 V RMS supply = 230 × √2 ≈ 325 V.
Formulas
RMS (sine)
V_rms = V_peak / √2
Real power
P = V I cos φ
φ phase angle
Frequency
f = 1 / T
T period
Practice questions
Q1.RMS value of a sine wave with peak 100 V?
AC Fundamentals · Easy
Q2.Power factor of a purely resistive load?
AC Fundamentals · Easy
Q3.Period of a 50 Hz supply?
AC Fundamentals · Medium