4.4

Efficiency = Useful Energy Out / Total Energy In x 100
Total Energy In = Useful Energy In (j)
Useful Energy Out = Useful Energy Out (j)
Efficiency = Efficiency (%)

1) Work out each every value.

Total Energy In =2000j
Useful Energy Out = 1000j
Heat Energy Out = 1200j
Sound Energy Out = 1400j

2) What is the kettle's efficiency?
Eff=UEO/UEIx100
Eff=1000/2000x100
Eff=50%