# Inductive and capacitive reactance

1. May 3, 2017

### fonz

Why is it that capacitive reactance is subtracted from inductive reactance and not the other way around when determining the overall reactance?

2. May 3, 2017

### magoo

What is the formula for capacitive reactance?

With a j in the denominator, the term becomes negative when you bring it to the numerator.

Understand?

3. May 4, 2017

### Staff: Mentor

Reactances in series add. Inductive reactance has a + associated with it, and capacitive reactance has a – associated with it. They keep these signs when you add them, and the result can end up being a net + or a net – depending on the magnitudes.

4. May 4, 2017

### jim hardy

Have you been yet introduced to phasor notation?

and it's related to the physical facts that
and
current lags voltage in inductors .

So a long long time ago the heavy thinkers {Steinmetz i think it was and Tesla picked right up on it)
decided that capacitance would get the minus sign and inductance the positive sign . Consistency kept their algebra simple. We never changed.

Be rigorous in your arithmetic and form good math habits. It'll pay off.

old jim

Last edited: May 4, 2017