# Direct Square Law Equation - Video Lesson

This lesson is about what we call the direct square law. It's also known as the mass maintenance formula. It's a simple calculation that explains to us as technologist, how we can change our mass when the SID is changing. And it's a simple relationship. If our SID is decreasing, then our mass also needs to decrease to maintain the same receptor exposure. If our distance is increasing, then our mass also needs to increase in order to maintain the same receptor exposure, So this is the basic form of the direct square law. This is the upper equation. Students can certainly use this equation, but I personally find the equation a little bit more helpful. And the reason for that is we can calculate our new mass or our new MA simply by multiplying the initial mass or the m a multiplied by the second distance squared over the first distance squared. So let's look at a few examples of how can use that in a practice problem. So here's practice problem number one. A radiograph is to be made using a seventy two inch SID using twelve mass. If the SID is

## Lesson Quiz

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