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Grade 11 · lesson 4 of 4

Choose an Energy Plan for a Defined Service

Compare plans that meet a requirement rather than only comparing watts.

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Supplied materials

  • Use the supplied fictional observations or model. Paper and pencil are optional; spoken answers are welcome. No equipment or real experiment is needed.

Learn the idea

An energy choice needs a service requirement. A plan with lower wattage can fail if it gives too little light or require more operating time. For our fictional reading display, the service must provide at least 600 recorded light-score units for 4 hours. Light-score is a supplied task measure, not a physical energy unit. Only plans meeting both service conditions are candidates.

Supplied plans are A: 20 W, light score 650, 4 h; B: 12 W, light score 500, 4 h; C: 15 W, light score 620, 4 h. Assume power and light score stay constant in each interval. A and C meet the requirement; B fails the light score. A uses 80 Wh and C 60 Wh, so C uses 20 Wh less for the required service. These fictional data do not recommend a real product.

  1. Mark which plans reach the 600 light-score threshold.
  2. Check the 4-hour duration for each.
  3. Calculate energy for A and C and compare.
  4. Choose among qualifying plans and explain why B is excluded.
Worked example

See the method in action

C provides score 620 for 4 h and uses 15×4 = 60 Wh. A uses 80 Wh for the same required duration. B uses only 48 Wh but its 500 score fails the stated service.

Your turn

Check your reasoning

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Which choice follows the supplied service requirement and minimizes energy among qualifying plans?

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See the answer and explanation

C, because it meets the service using 60 Wh

C meets both constraints and uses less energy than A. B is excluded by the minimum light score.

Take it further

Raise the required light score to 640. Only A now qualifies, using 80 Wh. A changed requirement can change the best eligible plan even when device data stay fixed.

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Check the subject sources

These LifeStarter passages, scenarios and exercises are authored for this Academy with AI assistance and review. External resources keep their publishers’ terms. A grade label suggests a starting level; it does not establish alignment with your school’s complete requirements.