Phasor Difference?

[ljcox]

Attached is an example from the book I mentioned.

Note that in 6.1 & 6.3, the applied voltage has zero phase angle so it is used as the reference phasor.

6.2 is more complicated. It may be useful for you to draw a phasor diagram of it. Note that, although they are using complex numbers, I think you should be able to draw the phasors.

In 6.1, note that the current is common to the source and both impedances.

 

[mel8030]

A phasor does not have to be referenced to 0 to get the right answer. It just makes getting the answer easier. For circuit problems, the math terms often subtract and divide out when one phasor is referenced to 0, important on exams to save time.
The current phasor is usally taken as the reference at 0 dergrees in series circuits
Supply voltage phasor is usually the 0 degree reference in parallel circuits..


phasors should be reserved for electrical applications.
phasor is short for" phase vector"
phasor are for magnitude and angle
vectors are more for direction and angle
vectors are used for velocity,torque and others
The terms, vectors and phasors are sometimes used interchangeably for electrical usage.

Hi mel8030

Now everyone,
In the attachment they haven't referenced one phasor to 0 zero--how come if that is the correct method?

Now the big one, what is the difference between a Phasor & a Vector seeing now that Vectors have been mentioned?

Thank You

 

[ljcox]

Attached are 3 pages that introduce vectors from my high school Physics book.

Sorry about the archaic imperial measurements, but it was before we changed to metric.

 

[codan]

Hi Everyone,

Thanks for the replies.

Len,

Thanks for posting the attachments.
You wrote:

"6.2 is more complicated. It may be useful for you to draw a phasor diagram of it. Note that, although they are using complex numbers, I think you should be able to draw the phasors."

I have to be honest & say i wasn't sure if i had to just draw the phasors & angles as stated in 6.2 or if i had to try to draw the phasors just for the Impedance & to work out the impedance of Z2 from that, which is what i did--i think?.

Anyway i gave it a go & i don't really understand about the (J) in everything so see how i go, if i have no idea i would rather know about it & fix the problem.
I'll attach the diagrams--GULP!.

Thank You

 

[ljcox]

That's very good.

The diagrams you drew are impedance diagrams not phasors. But they are correct.

I have attached the phasor diagram.

It shows the voltage and current phasors. There is no point in drawing it to scale except for the angles as there is only one voltage & one current.

If you drew the current phasor on the same scale as the voltage phasor, it would be very small. If you were to add another voltage phasor, it would have to be scaled the same as the 50 Volt phasor.

The j is the square root of -1. So j squared = -1 by definition. 5 + j8 is called a complex number. But this is fairly advanced maths, so I don't think you are ready for that level yet.

Have you gone to a municipal library or a library at a college?

 

[codan]

Hi Everybody,

Len,
Yes i drew the phasor diagram to start with using the values from problem 6.2 but thought it was to easy as the values etc were already stated & the problem was to find Z2. I was confused a little so i drew the Impedance as i had to work it out not knowing the math used.

I didn't know that the Impedance diagram i drew were not phasors though, i have just had a look at that & i found were someone has written that " although Z is complex, it is not a phasor as it is not a sinusoidal varying quantity."
So does that mean it is like resistance where it doesn't change the phase angle?

Yes i have gone to the libraries & the colleges i read what i can in the time allowed to borrow the books which is not long enough so i search the Net or ask things on the Forum, i don't ask everything on here as i would drive you all up the wall.

mel8030

Thanks for the explanation about phasors & vectors, i am slowly getting a grip on things.
There's lots to learn.

Thank You

 

[ljcox]

I have attached an impedance diagram for you.

In maths, they use i rather than j for the square root of -1.

They use j in electric maths since i is used for current.

 

[mel8030]

Hi Everybody,
I didn't know that the Impedance diagram i drew were not phasors though, i have just had a look at that & i found were someone has written that " although Z is complex, it is not a phasor as it is not a sinusoidal varying quantity."
So does that mean it is like resistance where it doesn't change the phase gle?
e
Y

It true that Z is really not a phasor. The term phasor is really just for voltage and current. This distinction is lost among many electrical engineers. They have never needed to think about it( I am not very clear about the distinction).
When using the polar form of Z, the magnitude Z comes with an angle so it will work as the go between for voltage phasor and current phasor. I think this is too much information for you at this stage . I recommend trying to be content doing the graphing and math at this stage. Deeper insight comes later.

I will try to give a beginners reason why you need the j stuff. In DC circuits, you can just add up the resistance of resistors for total resistance.. In AC, you just CAN'T add the resistance of resistors to the resistance of capacitor and inductors. You find the total with the use of complex numbers. The j keeps the values separate and reinforces the concept that you just cant add..

hey! this site talks about your vector subtraction.
**broken link removed**


Complex Numbers With Applications

 

[codan]

Hi Everybody,

Len,
Thanks for the impedance diagram & the calculation, it's very helpful.


mel8030

Thanks for that & the sites, they have some good info.

Well guys I can think of many times I have thanked everybody but the: Thanked 0 times to the left still remains, at least give it a 1 haha!

Thank You

 

[slimabidi]

You could make V1 the reference line, ie. make it the horiz line.