Overview
This lecture explains key energy concepts, types and units of energy, power, and the basics of energy conversions and thermodynamics.
Energy Concepts & Types
- Energy is the ability to do work or transfer heat.
- Energy exists as potential energy (due to position) and kinetic energy (due to motion).
- Chemical energy is a type of potential energy stored in chemical bonds.
- Electrical energy is a form of kinetic energy from moving electrons.
Conservation & Laws of Thermodynamics
- Energy is conserved; it cannot be created or destroyed (First Law of Thermodynamics).
- As energy converts from one form to another, some is lost as unusable heat, increasing entropy (Second Law of Thermodynamics).
Units & Conversions
- The SI unit of energy is the joule (J).
- 1 kilowatt-hour (kWh) = 3,600,000 joules (J).
- Other units include calories, kilocalories, BTUs, therms, and kilowatt-hours.
- 1 calorie = 4.184 J; 1 kilocalorie = 4,184 J.
- Power is the rate of energy use, measured in watts; 1 watt = 1 joule/second.
Dimensional Analysis & Example Problems
- To convert energy units, use dimensional analysis to cancel units step-by-step.
- Example: A Google search uses 0.003 kWh, equal to enough energy to run a 60 W bulb for 18 seconds.
- To find energy used by a device: multiply power (in watts) by time (in seconds), convert as needed to desired units.
Application: Light Bulb Problem
- To find energy used by a 75 W bulb in 24 hours:
- Convert power (watts) to joules (J) or kilojoules (kJ).
- Convert time from seconds to hours.
- Total energy = Power × Time, with proper unit conversions.
Key Terms & Definitions
- Energy — Ability to do work or transfer heat.
- Potential energy — Energy due to position.
- Kinetic energy — Energy due to motion.
- Joule (J) — SI unit of energy.
- Watt (W) — Unit of power; 1 W = 1 J/s.
- First Law of Thermodynamics — Energy is conserved.
- Second Law of Thermodynamics — Energy conversions increase entropy; some energy becomes heat.
Action Items / Next Steps
- Practice unit conversions involving energy and power.
- Attempt example problems converting between joules, kilowatt-hours, calories, etc.
- Review and understand both laws of thermodynamics.