Question

1. besides keeping your own electric bill low, list two other reasons for reducing your use of electricity.
2. 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.

Explanation:

Step1: Identify the formula for efficiency

The formula for efficiency is $\eta=\frac{\text{Useful Output Energy}}{\text{Input Energy}}\times100\%$.

Step2: Substitute the given values into the formula

Given that the useful output energy $E_{out}=190000\ J$ and the input energy $E_{in} = 240000\ J$.
Substitute into the formula: $\eta=\frac{190000}{240000}\times100\%$.

Step3: Calculate the value

$\frac{190000}{240000}\times100\%=\frac{19}{24}\times100\%$.
$19\div24\approx0.7917$.
$0.7917\times100\% = 79.17\%$.

Answer:

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