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Questions and Answers
What happens to the total energy supplied when a device operates at a certain efficiency?
What happens to the total energy supplied when a device operates at a certain efficiency?
- A portion of the energy is wasted, typically through heating. (correct)
- The total energy supplied decreases over time.
- All the supplied energy is converted into useful energy.
- The supplied energy becomes completely useful after installation.
When calculating payback time for energy-saving installations, which factor is NOT taken into consideration?
When calculating payback time for energy-saving installations, which factor is NOT taken into consideration?
- Cost of installation.
- Savings achieved per year.
- The environmental impact of the installation. (correct)
- The efficiency of the appliance.
In the context of efficiency, what is the significance of a Sankey diagram?
In the context of efficiency, what is the significance of a Sankey diagram?
- It represents both useful and wasted energy in visual form. (correct)
- It illustrates the cost of energy versus savings.
- It shows only the total energy supplied to a system.
- It provides a mathematical equation for calculating efficiency.
Which of the following statements accurately describes the distinction between accuracy and precision in measurements?
Which of the following statements accurately describes the distinction between accuracy and precision in measurements?
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How is the efficiency of a kettle calculated based on the given data?
How is the efficiency of a kettle calculated based on the given data?
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Study Notes
Efficiency
- Efficiency is the percentage of useful energy transferred.
- The efficiency of a device is calculated using the formula: efficiency = (useful energy transferred / total energy supplied) x 100%.
- A Sankey diagram can be used to represent energy transfers.
- The width of each arrow in a Sankey diagram represents the amount of energy.
- In a kettle, energy is stored in the hot water, the kettle itself, and the surroundings. All three represent energy loss.
Paying for Energy
- We pay for the amount of energy we use.
- Energy companies measure energy consumption in kilowatt-hours (kWh).
- One kWh is the amount of energy transferred when a 1 kW appliance is used for one hour.
- Reducing energy bills can be achieved through insulation and using more efficient appliances.
- Payback time is the length of time it takes for savings from energy efficiency improvements to pay back the cost of the improvements.
- Payback time can be calculated using: payback time = cost of change / savings per year.
Accuracy & Precision
- Accuracy refers to how close a measurement is to the true value.
- Precision refers to how consistent measurements are.
- Measuring devices with smaller divisions allow for more accurate measurements than devices with larger divisions.
- Precise measurements may not be accurate if the measuring instrument is not set up correctly.
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