Power

Lesson Objectives:

• Understand the concept of power and its relation to energy and time.
• Learn how to calculate power using the equation for power.
• Identify the unit of power and its abbreviations.
• Recognise the practical applications of power in real-world scenarios.

Key Points:

• Power is the rate of energy transfer or the rate at which work is done.
• The equation for power is P = energy/time or P = work/time.
• The unit for power is the watt (W), with energy and work measured in joules (J) and time in seconds (s).
• Power ratings are commonly used for electric appliances, motors, and engines.
• Power calculations involve considering power input and power output.
• Power can be used to determine the change in the thermal energy of a system.

Example Calculation:

• Scenario: Heating water with a Bunsen burner supplying 100 watts of power.
• Assumption: Water loses 30 watts of thermal energy to the surroundings (constant).
• Goal: Determine the change in thermal energy of the water after ten minutes.
• Calculation: Power input (100 watts) – Power output (30 watts) = 70 watts.
• Using the equation P = energy/time, calculate energy: 70 watts x 10 minutes x 60 seconds = 42,000 joules or 42 kilojoules.
• Conclusion: The thermal energy of the water increases by 42 kilojoules.

Takeaways:

• Power is a measure of the rate of energy transfer or work done.
• Power is expressed in watts (W), with energy and work in joules (J) and time in seconds (s).
• Power calculations involve considering input and output power.
• Power is widely used in various practical applications.