Question

1. an electric kettle uses 240 000 j of input energy to produce 190 000 j of useful output energy. calculate the percent efficiency of this electric appliance.
2. besides keeping your own electric bill low, list two other reasons for reducing your use of electricity.

Explanation:

Step1: Recall the formula for efficiency

The formula for percent efficiency ($\eta$) is $\eta=\frac{\text{Useful Output Energy}(E_{out})}{\text{Input Energy}(E_{in})}\times100\%$.

Step2: Substitute the given values into the formula

Given $E_{out} = 190000\ J$ and $E_{in}=240000\ J$. Then $\eta=\frac{190000}{240000}\times 100\%$.

Step3: Calculate the value

$\frac{190000}{240000}\times100\%=\frac{19}{24}\times100\%\approx 79.2\%$.

Answer:

The percent efficiency of the electric kettle is approximately $79.2\%$.