Power Dissipation — P = I²R = V²/R
Current Electricity
19
JEE Qs
8%
Hard
60
min
Carefully identify the voltage across and current through the specific component for which power dissipation is to be calculated.
🧮 Key Formulas
✅ Key Points for JEE
- 1Power (P) represents the rate at which electrical energy is converted into other forms (typically heat) by a resistor, measured in Watts (Joules per second).
- 2The choice between P=I^2R and P=V^2/R for calculations depends on the circuit configuration: use P=I^2R when current (I) is constant or easily determined (e.g., series connection), and P=V^2/R when voltage (V) is constant or easily determined (e.g., parallel connection).
- 3Power dissipation is directly responsible for the heating effect of electric current (Joule heating), where the total heat energy produced in time 't' is H = P*t = I^2Rt.
- 4Always use the current flowing *through* the specific resistor and the voltage *across* that specific resistor when calculating its individual power dissipation.
⚠️ Common Mistakes
- ✕Confusing the applicability of P=I^2R versus P=V^2/R; for series circuits, comparing resistors using P=I^2R is simpler, while for parallel circuits, P=V^2/R is simpler.
- ✕Using the total voltage of the source or total current from the source to calculate power dissipated by a single component, instead of the specific voltage across or current through that component.
- ✕Not understanding that the resistance 'R' in the formulas refers to the resistance of the component where power is being dissipated, not necessarily the total circuit resistance.
📝 Practice Questions
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NCERT Chapters
- Class 12 Physics Ch 3: Current Electricity