Calculating Energy Transferred by Electrical Appliances

Introduction

• Discussed how appliances transfer electrical energy into other forms (e.g., kinetic, thermal).
• Appliances have a power rating indicating energy transfer per second.
• Focus on using power ratings to calculate total energy transferred.

Key Equation

• Energy (Joules) = Power (Watts) x Time (Seconds)
• Equation not provided in exams; essential to memorize.

Example Questions

Question 1: Kettle

• Problem: Kettle with power rating of 2,200 W, used for 80 seconds.
• Calculation:
  • Energy = 2,200 W x 80 s = 176,000 Joules
  • Convert to kilojoules: 176,000 J / 1,000 = 176 kJ

Question 2: Fan

• Problem: Fan with power rating of 20 W, used for 1 hour.
• Calculation:
  • Convert 1 hour to seconds: 1 hour = 3,600 s
  • Energy = 20 W x 3,600 s = 72,000 Joules
  • Convert to kilojoules: 72 kJ

Question 3: Iron

• Problem: Iron used for 5 minutes, total energy of 600,000 Joules transferred.
• Goal: Calculate power of the iron.
• Calculation:
  • Convert minutes to seconds: 5 minutes = 300 s
  • Power = 600,000 J / 300 s = 2,000 W

Question 4: Blender

• Problem: Blender with power of 400 W, energy transfer of 48,000 Joules.
• Goal: Calculate time used.
• Calculation:
  • Time = 48,000 J / 400 W = 120 seconds

Conclusion

• Able to calculate energy transferred using power ratings and time.
• Further practice available in the Orion Workbook available online.