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An 850 W consumer coffee maker can make ...

An 850 W consumer coffee maker can make 10 cups (1.75 litres) of `80^(@)C` coffee from `20^(@)C` tap water in 10 minutes. What percentage of the electrical energy consumed actually makes it to the coffee?

Text Solution

Verified by Experts

The energy needed for heating of water
`Q_(out)=mcDeltaT=(1.75kg)(4200J//kg*K)(80-20^(@)C)=441,000J`
The, energy consumed by the device (electrical energy)
`W_("in")=Pt=(850W)(10"min")(60s//"min")=510,000J`
The ratio of these two quantities is the efficiency of the device
`eta=Q_("out")//W_("in")=(441,000J)//(510,000J)xx100=86.5%`.
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