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)

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

Thanks Kevin

 

The correct answer is -53.67 because the current lags the voltage (if you take voltage with an angle of 0).

 

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.

 

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.

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

 

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.