North Carolina Intox EC IR II Practice Exam

What is the relationship between breath alcohol concentration and the voltage produced by the fuel cell?

Voltage is independent of alcohol More alcohol results in higher voltage More alcohol results in lower voltage Voltage varies unpredictably

Correct Answer:

More alcohol results in higher voltage

Explanation:

In a fuel cell breathalyzer, the alcohol in the breath undergoes an electrochemical reaction at the sensor. The amount of alcohol present drives how fast electrons are produced—the current. More alcohol means more electrons per second, so the current increases. The instrument converts that current into a voltage reading (through its circuitry and the sensor’s load), so as breath alcohol concentration rises, the measured voltage also rises. In normal operating ranges the relationship is essentially direct, meaning higher alcohol gives higher voltage. Only at very high concentrations or with sensor saturation might the relationship level off or become nonlinear.

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