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7.5.4 Energy Efficiency

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Efficiency of Electrical Appliance

  1. The efficiency of an electrical appliance is given by the following equation eq1
  2. Normally, the efficiency of an electrical appliance is less than 100% due to the energy lost as heat and the work done against friction in a machine.


Example 1
A lamp is marked “240V, 50W”. If it produces a light output of 40W, what is the efficiency of the lamp?

Answer:


Example 2
An electric motor raises a mass of 2kg to a height of 5m in 10s. If the input current from a source of 12V is 2A, find the efficiency of the electric motor.

Answer:
Input power,
P = IV
P = (2)(12) = 24W

Output power




Steps to Save Electricity

  1. Use efficient lighting
  2. Buy efficient electric appliances.
  3. Use appliances with automatic power off function.
  4. Choose electrical appliances of sizes and features which best suit your needs.
  5. Proper utilization of all electrical appliances
    1. Defrost refrigerators regularly
    2. Run your washing machine only when it is fully loaded & Iron your clothes only when you have at least a few pieces to iron.
    3. Regular cleaning of air filters in air-condition units and clothes dryers.