# Homework Help: What is the reactance of the capacitor at 1.00 kHz?

1. Jul 17, 2005

### hotstuff

i seemto be frequenting this board more than i intended to but i physics is not my strong point at all so if i seem bothersome apologize about that and i also try to put what i have done sor for in the problem so it don;t seem like i am not trying so here goes and besides does anyone know where i can get a darn good physics tutor, one i can talk to over the phone?

A circuit consists of a 1.00 kHz generator and a capacitor. When the rms voltage of the generator is 0.550 V the rms current in the circuit is 0.460 mA.
(a) What is the reactance of the capacitor at 1.00 kHz?
k
(b) What is the capacitance of the capacitor?
µF
(c) If the rms voltage is maintained at 0.550 V, what is the rms current at 2.00 kHz?
mA
If the rms voltage is maintained at 0.550 V, what is the rms current at 10.0 kHz?
mA

1. to get the reactance first i derived c from eqn Irms= Vrms * wc
and then sub for Xc= 1/above ans which was 5.25)*2(3.140*1000hz
that should have given me the ans but the book says different

for the b capacitance, i used Xc= 1/wc

for c it should be irms= wCVIrms - right

thanks

2. Jul 17, 2005

### Päällikkö

I don't remember much about alternating current but, isn't impedance:
$$Z = \sqrt{R^2 + X^2} = \frac{V}{I}$$, where X is the total reactance ($$X_C + X_L$$).
As there's only a capacitor (and a generator) in the circuit the above equation solves into $$Z = \frac{V}{I} = X_C$$

You don't need $$X_C = \frac{1}{\omega C} = \frac{1}{2 \pi f C}$$ for a)