Key relationship
P=Vrms Irms cosφ=Irms²R; cosφ=R/Z.
Physics · Class 12
Power factor and reactive current
Voltage and current out of phase exchange energy with L and C. Their reactive components do not contribute net energy over a whole cycle; R consumes real power.
Open the interactive experiment →Power factor and reactive current
கட்ட வேறுபாடு காரணமாக AC ஆற்றல் பரிமாற்றம் மாறும். சராசரி உண்மை சக்தி Vrms Irms cosφ.
Key notes, relationships and model limits
Remember
Voltage and current out of phase exchange energy with L and C. Their reactive components do not contribute net energy over a whole cycle; R consumes real power.
Common trap
Average real power includes cosφ. A nonzero RMS current can have zero average power in an ideal purely reactive element.
Model limits
Positive R series LCR. Pure-reactance zero-power statement is a limiting case; plotted circuit retains finite R.
What you will learn
Use the controls and plotted relation to explain power factor and reactive current.
Try the experiment
Try both scenarios, change one control, and predict the result before checking the graph and readouts.
Think of it this way
Change one input while keeping the others fixed, as you would in a controlled experiment.
Worked example
At zero phase, cosφ=1. For Vrms=70.71 V and R=50 Ω at resonance, P=100 W.
Why this matters
The model connects power factor and reactive current with an observable reading. Check the equation and assumptions before applying it.
Before you start
SI units · algebra · graph reading
Check your understanding
Average power in an ideal pure reactive element over a whole cycle is?
- Vrms Irms with no phase factor.
- Zero; stored energy is returned to the source.
- Always negative over every full cycle.
Read the explanation
Zero; stored energy is returned to the source.
Course connection: Class XII Chapter 7. Consult the roadmap for CBSE, NEET, JEE Main and Advanced scope.