Lecture on Electrical Power

Introduction to Power

• Power Definition: Rate at which energy is used, transferred, or the rate at which work is done.
• Examples:
  • Walking vs Running up stairs: Same energy, running requires higher power due to quicker energy transfer.
  • Boiling water pots: Pot boiling quicker has higher power despite same energy input.
  • Engines: Higher horsepower engines convert chemical to kinetic energy faster.
• Electrical Power: Conversion of electrical energy to another form quickly.
  • Measured in watts.

Power in Electrical Devices

• High Power Applications: Require fast energy conversion.
  • Examples: Hairdryers, blenders, vacuum cleaners.
• Energy Consumption: Higher power devices consume more energy over time.
  • Example: Incandescent vs LED bulbs, LED uses a tenth of the energy.

Measuring Power

• Unit of Power: Watt (W) = Joule/Second (J/s).
• Power Equation: Power = Voltage x Current.
  • Voltage: Energy per unit charge.
  • Current: Rate of charge flow.

Calculating Electrical Power

• Ohm's Law: Allows substitution in power calculation.
  • Power = Voltage x Current.
  • Alternative formulas using resistance:
    • Power = V²/R (if current unknown)
    • Power = I²R (if voltage unknown)
• Example Calculation:
  • 60-watt bulb in a 120-volt outlet draws 0.5 amps.
  • Resistance calculation: V²/R gives 240 ohms.

Energy and Billing

• Kilowatt Hours (kWh): Unit of energy used for billing.
  • Power x Time = Energy.
• Cost Calculation:
  • Example: 575 kWh at $0.03 per kWh equals $16.
• Why kWh?: More practical than joules due to large energy amounts.

Cost of Electrical Appliances

• Example: 1,440-watt AC left on all day.
  • Calculations result in $4/day or $125/month.
• Energy Efficiency Tips:
  • Close blinds, seal windows to retain heat.
  • Use services like MassSave for efficiency improvements.

Conclusion

• Considerations: Power usage impacts energy consumption and costs.
• Advice: Use energy-efficient practices to save on bills.