Overview
This lecture explains the concept of power in physics, covers its definitions and formulas, and demonstrates calculations using practical examples.
Definitions and Formulas for Power
- Power is the rate at which energy is transferred or converted.
- First formula: Power = Energy Transferred / Time.
- Second formula: Power = Work Done / Time.
- Work done refers to energy transferred when a force moves an object a certain distance.
- Power is measured in watts (W), energy in joules (J), and time in seconds (s).
Distinguishing Work Done and Energy Transferred
- Work done is used when a force moves an object.
- Energy transferred is used when energy moves without force or movement (e.g., charging a phone).
Power Calculation Example (Lamps)
- Left lamp: 1,200 J transferred in 20 s → Power = 1,200 / 20 = 60 W.
- Right lamp: 1,500 J transferred in 30 s → Power = 1,500 / 30 = 50 W.
- The left lamp is more powerful.
Rearranging Power Equation (Microwave Example)
- Rearranged formula: Energy Transferred = Power × Time.
- 3 minutes converted to 180 seconds (3 × 60).
- Calculation: 1,100 W × 180 s = 198,000 J; convert to kJ = 198 kJ.
Power Calculation Example (Pushing a Car)
- Work done: 9 kJ = 9,000 J in 20 s.
- Power = 9,000 J / 20 s = 450 W.
Key Terms & Definitions
- Power — the rate at which energy is transferred or work is done.
- Work Done — energy transferred when a force moves an object over a distance.
- Joule (J) — unit of energy or work.
- Watt (W) — unit of power, equal to one joule per second.
Action Items / Next Steps
- Practice using the power formulas with real-life examples.
- Convert minutes to seconds when calculating power or energy.
- Visit the recommended website for additional questions, flashcards, and exam practice.