Power in Physics

Definition of Power

• Power is defined as the rate at which energy is transferred or the rate at which work is done.

Equations for Power

1. Power from Energy:
   • ( \text{Power (W)} = \frac{\text{Energy transferred (J)}}{\text{Time (s)}} )
2. Power from Work Done:
   • ( \text{Power (W)} = \frac{\text{Work done (J)}}{\text{Time (s)}} )

Unit of Power

• The unit for power is the Watt (W).
  • 1 Watt = 1 Joule per second.

Example Calculations

• Beaker Heating Example:
  • Two bunsen burners heating water:
    • Left burner: Transfers 250,000 J in 500 s
    • Right burner: Transfers 180,000 J in 500 s
  • Calculating Power:
    • Left burner: ( \frac{250,000 \text{ J}}{500 \text{ s}} = 500 \text{ W} )
    • Right burner: ( \frac{180,000 \text{ J}}{500 \text{ s}} = 360 \text{ W} )

Practice Questions

• Question 1:

  • Scenario: A car's brakes do 40,000 J of work in 5 s.
  • Calculate Power:
    • ( \text{Power} = \frac{40,000 \text{ J}}{5 \text{ s}} = 8,000 \text{ W} )

• Question 2:

  • Scenario: Two motors lifting masses:
    • Motor A: 500 J in 40 s
    • Motor B: 500 J in 60 s
  • Calculating Power:
    • Motor A: ( \frac{500 \text{ J}}{40 \text{ s}} = 12.5 \text{ W} )
    • Motor B: ( \frac{500 \text{ J}}{60 \text{ s}} \approx 8.3 \text{ W} ) (to one decimal place)

Additional Resources

• More questions available in a revision workbook accessible via the provided link in the video.

Summary

• You should now be able to describe power and calculate it using energy or work done.