ok so, the first problem i was able to apply the formula to get my answer but, the 2nd problem i don't understand why im not getting the answer. (which is 320 )
any suggestions as of different approach to this?

 

The answer isn't 320 as far as I can tell. I see 470 uf in series with 1 uf, and the answer to 2 caps in series is always less than the smallest capacitor. I see .9978769 uf on my calculator.

Still, I prefer a method that can do more than 2 capacitors, so don't get too invested in this formula. It's right for 2 caps, but life serves up different problems eventually.

 

The answer isn't 320 as far as I can tell. I see 470 uf in series with 1 uf, and the answer to 2 caps in series is always less than the smallest capacitor. I see .9978769 uf on my calculator.

Still, I prefer a method that can do more than 2 capacitors, so don't get too invested in this formula. It's right for 2 caps, but life serves up different problems eventually.

 

but, why are they showing an answer of 320?

 

Unit issues

470 nF is equal to 0.47 uF

Or, better to calculate it all out in nanoFarads instead of microfarads (uF)

So, 1uF = 1000 nF in series with 470 nF

Try again

 

It's the units labels that went wrong. You have to convert 1 uf to 1000 nf to get the formula to work.

 

 

Unit issues

470 nF is equal to 0.47 uF

Or, better to calculate it all out in nanoFarads instead of microfarads (uF)

So, 1uF = 1000 nF in series with 470 nF

Try again

so, i do 470÷1000 and 471÷1000?

 

(470 x 1000) /(470+1000)

 

Take reciprocal of c1 + reciprocal of C2

Then take the reciprocal of that total to get your answer

 

Take reciprocal of c1 + reciprocal of C2

Then take the reciprocal of that total to get your answer

That's the formula I was trying to think of in post #2. You can add up the 1/x's all day long, then 1/x the result to get the answer.

 

(470 x 1000) /(470+1000)

so, it's best to change the units? and than proceed?

 

so, i do 470÷1000 and 471÷1000?

 

but, why are they showing an answer of 320?

Because that's the correct answer.

If you track your units, you would have seen where you went wrong.

\(
\frac{470 \, nF \, \times \, 1 \, \mu F}{470 \, nF \, + \, 1 \, \mu F}
\)

Now when you look at the denominator you don't see 470 + 1, you see two things that can't be added together that way because they don't have the same units.

\(
\frac{470 \, nF \, \times \, 1 \, \mu F}{0.470 \, \mu F \, + \, 1 \, \mu F}
\)

NOW you can add the denominator

\(
\frac{470 \, (nF)(\mu F)}{1.470 \, (\mu F)}
\)

Now the uF cancel, leaving you with 320 nF.

Always, always, ALWAYS track your units!!!