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# Exposure and the Inverse Square Law

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The inverse square law has very practical applications.
a) If the exposure at d=30 cm from a point source is 1R, what is the exposure at d=5c from the source?
b) Suppose an acceptable chest radiograph was taken using 30mAs at 80kVp from 1m. Suppose that it was now requested that one be taken at 1.5m at 80kVp. What mAs setting should be used to yield the same exposure.

#### Solution Preview

The inverse square law has very important practical applications and is used very commonly in the real world. This is an important concept to understand because it is used so often and luckily it is very simple.

Very simply the inverse square law is physical law that states that the intensity of a specific value is inversely proportional to the distance squared.

The inverse square law is most easily understood while explicitly looking at an example. Often the inverse square law is used when say a detector of some sort is moved further away or closer to a radiation source giving you an decreased or increased exposure, dose, intensity, etc.

So in part A you are asked to find the exposure if the point source is moved from d = 30 cm to d = 5 cm. Since we are at a closer distance ...

#### Solution Summary

The solution examines the exposure and the inverse square law.

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