### Proportionality

This is the principle that if you have 2 variables their relationship will be constant.

The reason this is important is if you know a that two values are proportional to each other then if one is increased the other must be increased.

Take for example Frequency (Mhz) and Resolution. If you increase the frequency of an ultrasound transducer or the frequency of the pulse then you increase the resolution of the image.

Power is proportional to intensity. If you increase the power then you will increase the intensity.

### I = p / area

Remember from our post on formulas and formula conversions that whatever is on the top of the fraction will be proportional.

So if we have **Intensity** = **Power** / **Area**, then Intensity and Power are proportional. They have a direct relationship. One goes up the other goes up.

Knowing this really helps answer any question that revolves around values that we actually have a formula for. So if for example it asks “If the area of the Ultrasound beam is decreased what happens to the power and intensity?”. We know that if the area goes down then the intensity goes up (think of the focal point of the beam) so if intensity goes up then the power directed to that area will also increase.

If you have any questions please sound off in the comments.

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#### Franco

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Do you have any lectures on Intensities?

I don’t have a specific video on just intensities but there are a few posts that do deal with them.

http://www.examrefresh.com/decibels/

http://www.examrefresh.com/beam-dynamics/

Ok thank you. I will watch these. Study for the SPI. Taking in Novemeber. Have found this website very helpful. Thank you!

The premium package comes with what other helpful studies to pass this exam

The premium package comes with the study guide, videos, flash cards and unlimited practice tests. Also, I am available by email for all members.