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The degree of disturbance of a sample collected by a sampler is expressed by a term called the area ratio. If the outer diameter and inner diameter of the sampler are \(D_o\) and \(D_i\), respectively, the area ratio is given by

1. \((D_o^2-D_i^2)/D_i^2\)
2. \((D_i^2-D_o^2)/D_i^2\)
3. \((D_o^2-D_i^2)/D_o^2\)
4. \((D_i^2-D_o^2)/D_o^2\)

Correct answer: \((D_o^2-D_i^2)/D_i^2\)

Solution

The area ratio is defined as the ratio of the area of the sampler wall to the area of the sample inside the sampler, multiplied by 100 in some texts. In formula form, it is proportional to \((D_o^2-D_i^2)/D_i^2\). This measures the disturbance caused by the sampler.

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