# Capacitor and inductor reactance

Discussion in 'Electronics Homework Help' started by Zeeman2000, Mar 2, 2015.

1. ### Zeeman2000

6
1
Mar 2, 2015
Hello everyone,

I am currently working through a self study book on electronics. I have starting a chapter which is an introduction to Alternating Current. The chapter discusses capacitor and inductor reactance using the following formulas:

XL = 2pifL
XC = 1/2pifC

At the end of the chapter there is a self test which gives a value of a capacitor reactance and the value of a capacitor or inductor and asks to find the frequecy necessary to cause reactance.

The equation for this was not dicussed im the chapter. Can someone explain the equation needed to find the answer?

I tried the equation in reverse which worked for:

100Hz
10H

6.28 * 100 * 10 = 6280 ohms

6280 / 10 / 6.28 = 100Hz

In the self test the values are:

L = 50 μH, XL = 320 ohms, f =

320 / 50 / 6.28 = 1.019108280254777

Book answer was 1.02kHz

Not sure how they are getting this answer. Any help much appreciatted.

2. ### Laplace

1,252
184
Apr 4, 2010
Units in the formula are Ohm, Hertz, and Henry. 50 μH = 0.000050 H.

3. ### Zeeman2000

6
1
Mar 2, 2015
Yes, 50 μH = 0.000050 H

Turns out the question in the book was wrong. I have since checked the errata and it should have read 50mH not 50μH

As even using 0.000050 H gave and answer in MHz

4. ### BobK

7,682
1,688
Jan 5, 2010
Yep, at 50mH the answer in the book is right.

Bob

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