# Homework Help: Polar form of phasor

1. Apr 15, 2015

### sciman

Hello

Excuse me, but how do I sketch the phasor of a voltage that it's V=5cos(10t+30degrees) and how the V=5sin(10t+30degrees) ?

I know that these can be converted as the R<angle polar form, with R being the Vmax, ie the 5, and the angle the phase.

But what doesn't it matter if I have cos or sin???

thanks

2. Apr 15, 2015

### jldibble

Cosine is 90 degrees out of phase with sine.

3. Apr 15, 2015

### sciman

I know that

the problem is how do I represent the cos phasors with polar form complex number and how the sin phasors

4. Apr 15, 2015

### SammyS

Staff Emeritus
$\displaystyle e^{i\theta}=\cos(\theta)+i\sin(\theta)$

5. Apr 15, 2015

### sciman

I said polar form, not euler

6. Apr 15, 2015

### SammyS

Staff Emeritus
It is the basis for polar.

$\displaystyle 5\cos(\theta)=\text{Re}\left(5e^{i\theta}\right)$

7. Apr 15, 2015

### sciman

can you forget altogether Euler?
I only deal with rectangular and polar forms

8. Apr 15, 2015

### SammyS

Staff Emeritus
Excuse me.

9. Apr 15, 2015

### sciman

I don't know euler

the question is precise:

write in polar form: V=Vmaxsin(100t+30) and V=Vmaxcos(100t+30)

the problem is:
1) do I write Vmax<30 and Vmax<120 ?
2) do I write Vmax<-60 and Vmax<30 ?
something else?

10. Apr 15, 2015

### SammyS

Staff Emeritus
(In the green bar at the top of the Text Window: Use the X2 button for subscripts, the X2 button for superscripts. It makes V=Vmaxcos(100t+30) be more readable.

Click the big and you get to chose from a set of useful technical characters at the bottom of the text window, including ' ∠ ' . )

In my experience, it's customary to use cosine as the basis, i.e. zero phase, but I have seen sine used on occasion.

Vmax∠-60 and Vmax∠30 seems likely.

11. Apr 15, 2015

### sciman

but aren't these two differest sets of polar form numbers?
there should be a unique way, they cannot be both valid!

12. Apr 15, 2015

### SammyS

Staff Emeritus
It's not written on some great stone tablet that you must use cosine or that you must use sine.

If some author chooses an unconventional notation, he/she only need be consistent (and hopefully she/he warns the reader).