electronics.....can some one explain why phase angles can be plus or minus

[otispunkmeyer]

im working through some questions and so far i know that

for series the angle is arctan(Xc/R) and for parallel its arctan(R/Xc)

but sometimes i get the angle right but the sign is the opposite. i always get positive angles yet sometimes in the book they get minus angles and they simply fail to explain why.

any of you guys know?

 

[Calin]

Condensers and solenoids will change the phase in different directions. And serial and paralled will also change the phase in different directions (a condenser in parallel will change the phase is the same direction as a solenoid in series)
Or this way I remember from 1995, when I last studied these things

 

[FoBoT]

leading or lagging, there was an acronym we used, i wonder if i can remember it

or yeah, eli the ice man

ELI ICE

voltage lags current in inductors
current lags voltage in capacitors

 

[otispunkmeyer]

Originally posted by: FoBoT
leading or lagging, there was an acronym we used, i wonder if i can remember it

or yeah, eli the ice man

ELI ICE

voltage lags current in inductors
current lags voltage in capacitors

we use CIVIL

current leads voltage in caps
curren lags voltage in inductors

that right?

but i still dont get how some angles come out minus

i was asked to find the impedance and the phase angle.

i got 261 ohms for the impedance (which is correct)
then used

arctan (R/Xc) and got 79 ish degrees, but the answer is -79 degrees why?

 

[otispunkmeyer]

no one?

 

[FoBoT]

i can't remember anymore , it has been almost 20 years
and i don't use that stuff anymore in my job

 

[radioouman]

Originally posted by: otispunkmeyer

Originally posted by: FoBoT
leading or lagging, there was an acronym we used, i wonder if i can remember it

or yeah, eli the ice man

ELI ICE

voltage lags current in inductors
current lags voltage in capacitors

we use CIVIL

current leads voltage in caps
curren lags voltage in inductors

that right?

but i still dont get how some angles come out minus

i was asked to find the impedance and the phase angle.

i got 261 ohms for the impedance (which is correct)
then used

arctan (R/Xc) and got 79 ish degrees, but the answer is -79 degrees why?

I think that you just have to remember whether it is a capacitor or an inductor and use the minus as necessary.

 

[otispunkmeyer]

Originally posted by: radioouman

Originally posted by: otispunkmeyer

Originally posted by: FoBoT
leading or lagging, there was an acronym we used, i wonder if i can remember it

or yeah, eli the ice man

ELI ICE

voltage lags current in inductors
current lags voltage in capacitors

we use CIVIL

current leads voltage in caps
curren lags voltage in inductors

that right?

but i still dont get how some angles come out minus

i was asked to find the impedance and the phase angle.

i got 261 ohms for the impedance (which is correct)
then used

arctan (R/Xc) and got 79 ish degrees, but the answer is -79 degrees why?

I think that you just have to remember whether it is a capacitor or an inductor and use the minus as necessary.

the answers in this book seem to suggest otherwise, and the lecture notes are horrible...hes compressed 4 A4 sheets on to one A4 sheet with a photocopier

 

[dighn]

make sure you get the reactance right. it's -j(1/wc) for capacitors and jwl for inductors

so the angle would be arctan(R/Xc) where Xc must be negative