# Degrees vs. Radians



## Lielec11 (Aug 29, 2012)

Going thruogh some sample questions in the Camara "Power practice problems for the electrical and computer PE exam" review book, I've noticed that certain problems require you to use radians, while others you only get the correct answer when using degrees.

My questions is, how do I know when to use one or the other? There doesn't seem to be any reasoning either way.

Thanks.


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## Peele1 (Aug 29, 2012)

Practice, practice, practice.

A(circle) = pi r ^2

C = 2 pi r

360 degrees = 2 pi radians.

It's easy to convert back and forth. Some problems are a little easier (or can be done mentally) with degrees or radians. One of the tricks of the test is to check to see if you know the difference, and can use the tricks to work the problem faster. They also like 3-4-5 right triangles, and other such quick and no-calculator required problems.


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## ventilator (Aug 29, 2012)

What problems are you referring to? I don't remember having to use radians much if at all, maybe seeing the problems would jog my memory.


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## Wildsoldier PE (Aug 29, 2012)

When i started studying i had the same problem...but those kind of problems that require radian # are usually general electrical engineering problems(which usually is a waste of time working with them)...Most of the PPI problems are not fit for the Power module.....power is more based on degrees using numbers in polar and rectangular form. Dont trust too much the PPI books to get prepared(how ever is a good resourse for some topics only)......I will said take some time to study dont rush your studies...i took about a year and a half to prepare for the PE....i basically start from scratch...starting by reading my college books on single phase steady state ac analisys. After getting all the basics covered i started the GATech review course....and bought all the complex imaginary test....now there is another resourse like Spin-Up test....with all that material available and if you really want the PE....prepare an schedule on topics etc. you need to cover you shouldnt have any problems on passing. I passed the PE on my first try(Octuber 2011).....Passed the EIT on my third try in (April 2006)..!.....If I pass everyone can pass but requires hard work and true dedication....is not an imposible exam.


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## oilsands (Aug 30, 2012)

I am not an electrical engineer and please take this with a grain of salt.

Radians have no units, as they are length-to-length ratio, so basically working out the units should help to figure out what to use. A good example from math: circular segment area is A=[r^2(Angle-sin(Angle)]/2, and one should use radians here to get m^2, otherwise you get m^2*(degree - sin(degree)) which makes no sense.

Again, I have no idea how it applies to your electrical problems, but may be in a similar way.


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