Easyphysics
GCSE - OCR 21 Century
P3 Radioactive Materials

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The Energy-Saver light bulb is 5 times more efficient than an ordinary filament bulb.

 
       

 P3 Efficiency   

Syllabus Summary Questions Answers

      

       Efficiency = (useful energy transferred by the device)  ÷  (total energy supplied to the device) 

  • The greater the percentage of the energy that is usefully transformed in a device, the more

    efficient the device is.

  • Example: Electric kettle

 

Efficiency

=

180 000 J

200,000 J

 

Efficiency

=

0.9

 

Percentage Efficiency

=

180 000 J x 100 %

200 000 J

 

Percentage Efficiency

=

90 %

      Generating and delivering electricity is not 100% efficient.

         Energy is lost to the environment at each stage as shown in the following Sankey diagram.