Study guide: Energy pathways and honest energy budgets
Trace energy and check that a simplified energy ledger accounts for inputs.
Ideas to explain in your own words
- Explain a simple energy pathway without claiming energy is created.
- Check a simple energy budget without losing or creating energy.
- Use equal inputs to compare outputs for one stated purpose.
- Use a system boundary and storage change to complete a ledger.
Watch your reasoning
- The battery supplies stored energy. The circuit transfers energy to the light source, which gives off light and also thermal energy. The model neither creates energy nor claims all the energy becomes light.
- All 30 input units must be accounted for. 30 − 9 = 21 thermal units under the stated two-output, no-storage-change model.
- The inputs match and B’s light output exceeds A’s by 6 units. Both total outputs still equal 40.
- Outputs total 15, so 18 − 15 = 3 units remain as the storage increase under these conditions.
A worked review example
Trace Energy through a Flashlight: A checked description is: battery’s stored chemical energy → electrical energy in the circuit → light and thermal energy transferred to the surroundings. Account for the Flashlight’s Outputs: The outputs total 6 + 14 = 20 units, equal to the input. Six units serve the lighting goal, while 14 transfer as thermal energy; none is treated as disappearing. Compare Useful Outputs Fairly: A: 10 + 30 = 40. B: 16 + 24 = 40. B transfers 16 − 10 = 6 additional light units for the same input; it also transfers fewer thermal units. Find the Missing Energy Entry: 8 light + 12 thermal out + 5 stored = 25 input units. The device has more stored energy at the interval’s end; the outside outputs alone total 20.
Make a practice plan
- Try the supplied lesson problems without looking at the answers.
- Compare your method with the worked examples and explain any correction.
- Use the new review cases, then complete the transfer task on paper or in your own document.