#### scubasteve_911

Joined Dec 27, 2007
1,203
In this case you can use use c^2=a^2 + b^2 for the magnitude of the resultant vector, then use any trig identity to solve for the angle.

theta = arctan(8/6)

#### Ratch

Joined Mar 20, 2007
1,070
Hawkeye87,

Although the reference you cited talks about vectors, voltage is not a vector quantity. It has magnitide but not direction. Alternating voltages can be represented by phasors, which have magnitude and an angular relationship between them. Phasors also have some vector like properties, but not all of them. To add voltage phasors, split up each into real and orthogonal parts. Add up the real parts and the orthogonal parts. Then convert back to polar form if desired, or leave it like it is. scubasteve_911 touched on how to convert to polar form.

Ratch

#### Hawkeye87

Joined Oct 7, 2008
52
I figured out that question and i now have yet another....
If
V1 = 80sin(ωt + 25°)
V2 = 10sin(ωt - 15°)
find the sum Vt=V1+V2 where the angular velocity (ω) is 400.
Where do you start?

#### Ratch

Joined Mar 20, 2007
1,070
Hawkeye87,

I figured out that question and i now have yet another....
If
V1 = 80sin(ωt + 25°)
V2 = 10sin(ωt - 15°)
find the sum Vt=V1+V2 where the angular velocity (ω) is 400.
Where do you start?
Angular velocity is irrelevant, so long as it is the same for both voltages.

80/_25 = 72.50 +j33.81
10/_-15 = 9.66 +j-2.59

72.50+9.66 + j33.81-j2.59 = 82.16 + j31.22 = 87.90/_20.81

Ratch

#### Hawkeye87

Joined Oct 7, 2008
52
now how would i calculate the frequency, period, peak to peak voltage of V1, the rms voltage of V2, the phase difference between V1 and V1 and the time difference between the two. Just set me up the equations and i'll have at it.

#### Ratch

Joined Mar 20, 2007
1,070
Hawkeye87,

now how would i calculate the frequency
2*Pi*f = w = 400

P = 1/f

peak to peak voltage of V1, the rms voltage of V2
You have to specify what the voltages given were.

the phase difference between V1 and V1
25 degrees - 15 degrees = 10 degrees

and the time difference between the two.
(10/360)*P

Just set me up the equations and i'll have at it.
I feel so guilty and ashamed for "helping" you so much. You will probably flunk out unless you can do problems like this yourself.

Ratch

#### Hawkeye87

Joined Oct 7, 2008
52
don't feel guilty. your helping someone who has a test friday that knows maybe half this. So consider the fact that your aiding my learning process by filling in the gaps that the teacher leaves out.

#### The Electrician

Joined Oct 9, 2007
2,751
Hawkeye87,

Although the reference you cited talks about vectors, voltage is not a vector quantity. It has magnitide but not direction. Alternating voltages can be represented by phasors, which have magnitude and an angular relationship between them. Phasors also have some vector like properties, but not all of them. To add voltage phasors, split up each into real and orthogonal parts. Add up the real parts and the orthogonal parts. Then convert back to polar form if desired, or leave it like it is. scubasteve_911 touched on how to convert to polar form.

Ratch
Ratch, do you see anything wrong with the first paragraph on this page:

http://en.wikipedia.org/wiki/Phasor

Last edited by a moderator:

#### Ratch

Joined Mar 20, 2007
1,070

#### thingmaker3

Joined May 16, 2005
5,084
Back on topic, if you please, gentlemen. Let's help the O.P. with complex numbers, not argue about semantics.

Ratch: if you have a problem with the AAC website, make your comment in the appropriate forum - this one is for helping folk with homework.

#### Ratch

Joined Mar 20, 2007
1,070
thingmaker3,

Let's help the O.P. with complex numbers, not argue about semantics.
I did help the OP, perhaps more that I should have. It is not a matter of semantics, it is about facts. Voltage is not a vector quantity.

Ratch: if you have a problem with the AAC website, make your comment in the appropriate forum - this one is for helping folk with homework.
I did not dwell on the mistake in the AAC, just a quick remark to get the OP on the right track. Which was helping him with his homework.

Ratch