add power factor

uni/mmme/2051_electromechanical_devices/ac_power.md

@@ -8,6 +8,8 @@ lecture_slides: [ ./lecture_slides/MMME2051EMD_Lecture3B.pdf ]
 exercise_sheets: [ ./exercise_sheets/Exercise Sheet 4 - Power factor and three phase.pdf ]
 ---
 
+This section builds on [introduction to AC](/permalink?uuid=0c90c691-cbf8-43e9-bfa5-7b277c853151).
+
 # Definitions
 
 - Phase voltage - voltage across any phase
@@ -49,3 +51,7 @@ $$I_\text{line} = I_\text{phase}$$
 $$|V_\text{line}| = |V_\text{phase}|$$
 
 $$I_\text{line} = \sqrt 3 I_\text{phase}$$
+
+# Power Factor (PF)
+
+$$\text{PF} = \cos{\gamma} = \cos{\left(\Phi_v-\Phi_i\right)}$$