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Questions and Answers
What is the efficiency of a kettle that transfers 1600 J of useful energy from a total of 2000 J supplied?
Which of the following actions can help reduce electricity bills?
How is accuracy defined in measurement?
What does the term 'payback time' refer to in the context of energy efficiency?
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A measuring device has the ability to provide similar readings over multiple trials. What characteristic does this device demonstrate?
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Study Notes
Efficiency
- Not all energy is transferred usefully.
- Wasted energy is often transferred by heating.
- The percentage of useful energy produced by something is known as its efficiency.
- Efficiency Formula: efficiency = $\frac{useful\ energy\ transferred}{total\ energy\ supplied} \times 100%$
- The width of an arrow in a Sankey diagram shows the amount of energy it represents.
- The energy stored in the kettle and the surroundings is wasted energy.
- Kettle Efficiency Calculation: efficiency of kettle = $\frac{1600\ J}{2000\ J} \times 100%$ = 80%
Paying for Energy
- We pay for the amount of energy we use in our homes.
- Electricity companies use units of kilowatt-hours on electricity bills.
- One kilowatt-hour is the amount of energy transferred when a one kW appliance is used for one hour.
- We can reduce bills by insulating our homes and by using more efficient appliances.
- The payback time of installing something that makes a home more energy efficient is the time it takes for the cost of installation to be matched by the money saved.
- Sometimes buying a more efficient appliance may not save you energy overall because it costs more to buy than it will save.
- Payback Time Formula: payback time = $\frac{cost\ of\ change}{savings\ per\ year}$
Accuracy and Precision
- A measurement is accurate if it is close to the true value of the thing being measured.
- Measuring devices that have small divisions can measure more accurately than instruments with larger divisions if they are set up correctly.
- A measurement is precise if several measurements of the same thing give similar results.
- Precise measurements may not be accurate if the measuring instrument was not set up correctly.
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Description
This quiz explores the concepts of energy efficiency and the financial implications of energy usage in homes. Learn about the efficiency formula, how to calculate the efficiency of appliances, and strategies for reducing energy costs. Test your knowledge on the impact of energy-efficient practices on electricity bills.
