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AC Phasor Diagrams
AP Physics C · E&M — AC Circuits
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Learning Objectives
Read voltage phasor diagrams for R, L, C components
Understand V_R in phase with I, V_L leads by 90°, V_C lags by 90°
Compute phase angle φ = arctan((X_L − X_C)/R)
Calculate power factor: cos φ
Key Equations
V = IZ, φ = arctan((X_L−X_C)/R)
V_R = IR (in phase)
V_L = IX_L (leads 90°)
V_C = IX_C (lags 90°)
Power = IV cos φ
Tags
phasor
AC circuit
impedance
phase angle
AP Physics C E&M
φ
0°
cos φ
0
ω (rad/s)
100
R (Ω)
50
L (mH)
200
C (μF)
50
V₀ (V)
120
Results
X_L
0
X_C
0
Z
0
I
0
φ
0
Power Factor
0
Quick Quiz
In an AC circuit, current through a capacitor:
Leads voltage by 90°
Lags voltage by 90°
Is in phase with voltage
Leads voltage by 180°