I was following an example that was using KVL to calculate the Voltage across A/B.
The way they did it was to assume the current was flowing like this :
Vr1 = 4.5v (using the R1/R2 divider)
Vr3 = 13.5v (using the R3/R4 divider)
And then calculate the top right loop using KVL, going clockwise :
Vr3 + Vab - Vr1 = 0
Vab = -Vr3 + Vr1
Vab = -13.5 + 4.5
Vab = -9v
I've been reading though, that if you don't know the current direction, you can just assume a direction, and that as long as you stay consistant, the value will still come out correct. You'll just have to remember the direction is actually flipped if you get a negative current.
So I thought I'd try a different current direction.
But I get a different result using KVL :
Vr3 + Vab + Vr1 = 0
Vab = Vr3 + Vr1
Vab = 13.5 + 4.5
Vab = 18v
Have a misunderstood something here? .. I appreciate that in the above example the currenly is clearly going the other way, but I wanted to just try a different direction as I understood the direction could be arbitrary?
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