# How to write 100 and -100 in phasor notaion

1. Jun 12, 2013

### eatsleep

1. Write the following signals in phasor notation: v7(t)=100, v8(t)=-100(

2. Acos(wt + Θ) = Ae^(j Θ)

3. I want to say 0 because its just a constant, if not then 1 because Θ=0. It seems to easy. Is it 0?

2. Jun 12, 2013

### Staff: Mentor

If it's an AC voltage with 0° phase shift, then the 100V source is just 100V ∠ 0°. The -100V source can be written as -100V, or alternatively, 100V ∠180°. Often, when the angle is 0 or 180 the shorthand 100V or -100V is adequate, so long as you make sure to specify clearly that it's a phasor value.

EDIT: As rude man points out in his (the next) post, phasor magnitudes are generally taken to be RMS values. If your given values of 100 and -100 are peak values of the sinusoid, then convert to RMS.

Last edited: Jun 12, 2013
3. Jun 12, 2013

### rude man

If a voltage in the time domain is v(t) = v0 sin(wt + θ) then the phasor is
V = (v0/√2)e.

So your equation 2 is off by a factor √2 and in 3 if the voltages are dc then there is no phasor at all since there is no sinusoidal voltage.

Phasors are applicable only for steady-state sinusoids.

If v7 = 100 sin(wt) or -100sin(wt) then the above should provide you your answers.