Working out Impediance need help!

**Mikeymike77** · 04-07-2009

Hey I am trying to do this formula but I can't work out the last number to get answer the bit I can't do is the 10-6 to get the answer.

frequency of 1 KHZ

2x3.142x1000 x220x10-6 - = 723.4ohms

Frequency 20 KHZ

2x3.142x20000x220x10-9 = 36.2ohms

Can anyone describe how to do the last number? Because on a calculater I don't the same number in ohms ?

**electricAl** · 04-07-2009

Where to start?

What is this, a given answer or fruit of your efforts?

The top calc is correct - but only if you square (you`ve written "x2"

)

The 3.142 gave it away, as in, you`d use Pi x r to the power of 2 (squared) but instead you`re using a Hz value.

Also, you`d need to substitute 230 instead of your 220 - i guessed this was Voltage (again you kept us in the dark

)

The `bit` you say you`re stuck on - the `to the power of -6` part was the easy bit

x10 -6 is 1 micro units (whatever you`re working in) In other words it`s 10 /10 with 6 zero`s after it (10,000,000) The minus symbol indicates you must invert the x into divide.

Therefore in the 2nd calc, the x10 -9 will be in nano units (10 /10,000,000,000) Just basic scientific notation

Unfortunately, knowing that doesn`t really help tho` as the 2nd calc is screwed up somehow - have you an idea i wonder?

Let us know if you figure out where.

Hope this helps

**Lenny** · 04-07-2009

Hi.

I been looking at your calcs for a while now and I think theres deffo something wrong with calc 2 somewhere.

I cant put my finger on it just yet as I dont have all the info i.e the original calc/question.

Anything with a - in fornt must be divided to gain the base unit unit i.e 10-6 would be 10,000,000 as a base unit - a micro unit.

Cheers.

ElectricAl beat me to it.

**electricAl** · 04-07-2009

Great minds & all that...

but

back to ya Lenny

**mechelec** · 05-07-2009

The first one is an inductance ie 2times pie, times frequency, times inductor. The second is capacitance, and the answer should be, one over, 2 times pie, times frequency, times capacitor. This gives 36.172 ohms which is near enough for anybody.

**eskimo39** · 06-07-2009

I thought when working out impediance you needed first to work out both Inductive Resistance and then Capacitive resistance.

Inductive Resistance is:

XL = 2*pi*f*L

Where f is Frequency (Hz) and L is Inductance (H)

Capacitive Resistance is:

XC =

1
-------------
2*pi*f*C

Where f is Frequency and C is capacitance (farads)

You then need the formular : Z = Sqrt R2 + (XL - XC)2

Is this correct?

**zupos40** · 06-07-2009

Originally Posted by Mikeymike77

Hey I am trying to do this formula but I can't work out the last number to get answer the bit I can't do is the 10-6 to get the answer.

frequency of 1 KHZ

2x3.142x1000 x220x10-6 - = 723.4ohms

Frequency 20 KHZ

2x3.142x20000x220x10-9 = 36.2ohms

Can anyone describe how to do the last number? Because on a calculater I don't the same number in ohms ?

it is

Capacitive Resistance is:

XC =

1
-------------
2*pi*f*C

Where f is Frequency and C is capacitance (farads)

And your answer to question 1 is incorrect decimal in wrong place, Answer = 0.7234 (I bet if you look at calculator 723.4 has a 10-4 to top right of answer.

Question 2. answer correct this is how I got it 100,000,000 / (2 x 3.142 x 20000 x 220) = 36.1715 ohms

The 100,000,000 represent convertion of 1/10-9

**mechelec** · 06-07-2009

Originally Posted by zupos40

it is

Capacitive Resistance is:

XC =

1
-------------
2*pi*f*C

Where f is Frequency and C is capacitance (farads)

And your answer to question 1 is incorrect decimal in wrong place, Answer = 0.7234 (I bet if you look at calculator 723.4 has a 10-4 to top right of answer.

Question 2. answer correct this is how I got it 100,000,000 / (2 x 3.142 x 20000 x 220) = 36.1715 ohms

The 100,000,000 represent convertion of 1/10-9

That is one way of doing it but very easy to make a mistake. You really need a calculator with an exponent key (ie. exp, ee) depending on your make and model.

**zupos40** · 06-07-2009

Originally Posted by mechelec

The first one is an inductance ie 2times pie, times frequency, times inductor. The second is capacitance, and the answer should be, one over, 2 times pie, times frequency, times capacitor. This gives 36.172 ohms which is near enough for anybody.

mike I think they are both calculation to find different Xc, if you do Xl for first question ans= 1.3824 ohms

Did not have calculator available, so i did it long hand.

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