Calculating Energy Transferred by Electrical Appliances

Introduction

• Purpose: Learn how to calculate the energy transferred by electrical appliances using their power ratings.
• Background: Power ratings indicate how many joules of energy are transferred every second.
• Focus: Use these ratings to calculate total energy transferred when an appliance is in use.

Key Equation

• Energy (Joules) = Power (Watts) × Time (Seconds)
• This equation is crucial and must be memorized, as it is not provided in exams.

Example Calculations

Example 1: Kettle

• Problem: A kettle with a power rating of 2,200 watts is used for 80 seconds.
• Solution:
  • Use the formula: Energy = Power × Time.
  • Energy = 2,200 W × 80 s = 176,000 Joules.
  • Convert to kilojoules: 176,000 J ÷ 1,000 = 176 kJ.

Example 2: Fan

• Problem: A fan with a power rating of 20 watts is used for 1 hour.
• Solution:
  • Convert time: 1 hour = 3,600 seconds.
  • Energy = 20 W × 3,600 s = 72,000 Joules or 72 kJ.

Example 3: Iron

• Problem: An iron uses 600,000 Joules in 5 minutes. What is its power?
• Solution:
  • Convert time: 5 minutes = 300 seconds.
  • Power = Energy ÷ Time = 600,000 J ÷ 300 s = 2,000 Watts.

Example 4: Blender

• Problem: A blender uses 48,000 Joules with a power of 400 watts. Calculate usage time.
• Solution:
  • Time = Energy ÷ Power = 48,000 J ÷ 400 W = 120 seconds.

Practice and Resources

• Practice questions are available in the Orion workbook.
• Link provided in the original lesson for additional exercises.

Conclusion

• The lesson provides the skills to calculate energy transferred using the power rating and time.
• Further practice is encouraged to master these calculations.