Use supplied input and output values to complete simple energy accounts.
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Method and worked examples
A complete simplified energy account lists input and all outputs. With no change in stored energy, total output equals total input. Add motion, heating and sound outputs before comparing with the input. In a two-output model, find a missing output by subtracting the known one from the input.
Use values for the same time interval and compatible energy units. If 80J enters and 50J goes to the intended output, the other stated outputs total 30J. Energy called wasted is still transferred somewhere, often into heating of surroundings. It belongs in the complete account even when it does not serve the device’s purpose.
Example 1
A motor receives 100J. Its stated outputs are 70J motion and 5J sound. Find the remaining heating output.
Heating =100−70−5=25J in the complete stated account.
Example 2
A lamp transfers 12J as light and 48J as heating. Find total output.
12+48=60J.
Watch out:All outputs count. Thermal and sound transfers remain energy even when they are not the intended output.
Reading energy-flow data practice | Year 8 Science | Ascent Arcade