Understanding Phasors: How to Sketch a Voltage Phasor in Polar Form

[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

 

[jldibble]

Cosine is 90 degrees out of phase with sine.

 

[sciman]

Cosine is 90 degrees out of phase with sine.

I know that

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

 

[SammyS]

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

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

 

[sciman]

I said polar form, not euler

 

[SammyS]

I said polar form, not Euler

It is the basis for polar.

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

 

[sciman]

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

 

[SammyS]

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

Excuse me.

 

[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?

 

[SammyS]

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?

(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=V_maxcos(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.

V_max∠-60 and V_max∠30 seems likely.

 

[sciman]

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

 

[SammyS]

(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=V_maxcos(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.

V_max∠-60 and V_max∠30 seems likely.

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).