1.1.10 Power

• Power


  The rate at which energy is transferred or work is done
• Power tells us how quickly something happens, whether it’s the transfer of energy or the completion of a task
• Unit of power

  The watt (W), where 1 watt equals 1 joule of energy transferred per second (1 W = 1 J/s)
• General Power Formula

  P=E/t
• Where in General Power Formula


  P is the power in watts (W)<|>E is the energy transferred in joules (J)<|>t is the time taken in seconds (s)
• Power in Terms of Work Done

  P=W/t
• Where in Power in Terms of Work Done


  P is the power in watts (W)<|>W is the work done in joules (J)<|>t is the time taken in seconds (s)
• Electrical Power Formula

  P=IV
• Where in Electrical Power Formula

  P is the power in watts (W)<|>I is the current in amperes (A)<|>V is the potential difference (voltage) in volts (V)
• Mechanical Power


  • Example: Lifting a weight
• Calculating Power Example

  1. Work done (W) = mgh

  2. Power (P) = W/t
• Work done (W) = 50 kg × 9.8 m/s² × 2 m = 980 J
• Power (P) = 980 J / 4 s = 245 W
• Electrical Power


  • Example: A 100 W light bulb
• Finding Current Example


  I=P/V
• Rearranging gives I=100W/230V≈0.43A
• Comparing Power

  • Example: Two engines
• Engine A transfers 1000 J of energy in 10 seconds (Power = 100 W)
• Engine B transfers 1000 J of energy in 5 seconds (Power = 200 W)
• Even though both engines do the same amount of work, Engine B is more powerful because it does the work in less time
• Efficiency

  Relates power to how much useful energy is transferred by a device compared to the total energy it consumes
• Efficiency Formula

  Efficiency = Useful Power Output / Total Power Input × 100%
• High-efficiency device

  • Converts a greater proportion of input energy into useful output energy, reducing waste
• Energy used in 5 minutes = 600,000 joules