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12.4: Complete Memo Example

  • Page ID
    142472

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    13.4 A Complete Memo Example — Annotated

    Here is a complete six-section memo addressing the resistor safety question from Chapter 11. Notice what it accomplishes in under one page.

    ENGINEERING MEMORANDUM

    To: ENGR 110 Instructor

    From: [Student Name]

    Date: [Date]

    Subject: Resistor Power Rating Evaluation — 12 V Source, 330 Ω Resistor


    1. Purpose

    This memo evaluates whether a 330 Ω resistor rated at 0.25 W is safe for use in a 12 V DC circuit. The analysis determines actual power dissipation, compares it to the rated limit, and provides a component recommendation.

    2. Background

    The circuit consists of a 12 V DC source in series with a single 330 Ω resistor rated at 0.25 W maximum continuous power. Assumptions: ideal resistor (constant resistance), DC source, steady-state conditions only.

    3. Methodology

    Power dissipation was computed using \(P = V^2/R\), derived from Ohm's Law and the power relationship \(P = VI\). No parameter sweep was required; the operating condition is a single fixed voltage.

    4. Results

    \[ P = \frac{V^2}{R} = \frac{(12 \text{ V})^2}{330 \text{ Ω}} = \frac{144}{330} = 0.436 \text{ W} \nonumber \]

    5. Analysis

    The computed dissipation of 0.436 W exceeds the 0.25 W rating by 74%. Operating at this condition would cause the resistor to overheat and potentially fail. The current drawn (\(I = 12/330 = 36.4\) mA) is reasonable for signal circuits, but the power constraint is the binding limit.

    6. Conclusion and Recommendation

    The 330 Ω, 0.25 W resistor is not safe at 12 V. A minimum rating of 0.5 W is required. Alternatively, resistance could be increased to 620 Ω (next standard value above 576 Ω) to stay below 0.25 W. Limitation: this analysis assumes steady-state DC; transient or AC conditions require additional analysis.


    This page titled 12.4: Complete Memo Example was last modified on Thu, 24 Sep 2026 17:38:16 GMT and is shared under a CC BY-NC license and was authored, remixed, and/or curated by .

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