# Help with Phase Angle calculation

Discussion in 'Math' started by kevinaussie, Jan 26, 2009.

1. ### kevinaussie Thread Starter New Member

Jan 26, 2009
1
0
I am doing a practice Test.

The question is what is the Phase angle between the V and I
XL=27.2 and R= 20
Phase angle = arctan (XL/R)
arctan(27.2/20)

I get arctan(1.36)
or 53.67
that is the wrong answer on my test!

Thanks Kevin

2. ### mik3 Senior Member

Feb 4, 2008
4,846
70
The correct answer is -53.67 because the current lags the voltage (if you take voltage with an angle of 0).

Dec 23, 2008
1
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u did not mention the voltage is taken across what R or L?

if its R, then the ans is -58 as mik said. or if its across L, then the answer is 90-58. if its across both R,L then the answer is 0.

4. ### dig1 Member

Jul 31, 2008
18
0
i am intrigued by this explanation... can somebody please lay out the fundamental equation for why this is a negative number,.... thanks

5. ### mik3 Senior Member

Feb 4, 2008
4,846
70
If you take the voltage wave form as the reference (ie 0 phase angle) then if the current lags the voltage (case of inductive load) the current will be delayed some degrees. Thus, the current reaches its peak value after a while the voltage does and and this suggests a negative angle with respect to the voltage.