ANY HELP ON THESE QUESTIONS ?

[jenko]

hi guys im stuying electriconic principles in school can anyone give me some pointers on how to:

1. a capacitor is connected across a 100v supply find the energy and charge if its value is 20uF

this is what i found : W=1/2(vxc)
100x0.020=2
2x1/2=1 watt
is this correct what have i found the charge or the energy :?: how do i find the other one:?:

2. i have been asked to find the 3rd value of a capacitor in series which will give the capacitence of 3 µf the two values are 10µf and 15µf
(no idea)

3. 3 capacitors in series 5µf 10µf 15µf across a 100v supply find the equivitiant capacity, the charge and voltage of each capacitor?
(no idea)

4. circuit has the capacitence of 30µf it is reduced to 10µf what value capacitor is required and how would you connect it ?
(not a clue again)

5. 3 capacitors 10 15 25µf in parallel across 120v calculate the equiviliant charge and capacitence of each capacitor?
(im ashamed of myself now)

6. present chare on 3 capacitors connected in parelle across a 50v supply 80 500 1400 whats the value of the capacitors and the equiviliant capacitence of the combination

7. the flux density between two curcular plates each radius of 200mm is 10µf what is the charge of the plates

8.a metal sphere insulated from earth carries a charge 0.25µC. the radius of the sphere is 150mm what is the feild strength at the surface of the sphere
is this the write equation= 4(TL = Pie)= 3.142 R²

9. what is the charge on a 8µf capacitor when the v is 250v?

10. capacitor carries a charge of 100µC when 100v is applied what is the capacitence ?


:|:|

IM REALY SORRY FOR THIS THREAD I HAVE LOOKED ON THE INTERNET AND COULDNT FIND MUCH CAN ANYONE GIVE ME LINKS TO WEBSITES THAT MAY HELP ME OR GIVE ME SOME INFOMATION ON THESE QUESTIONS I WOULD BE VERY GRATEFUL

BIG THANK YOU JENKO!

 

[Old Nick]

1 the energy in a capacitor is given by 1/2CV^2
2 capacitors in series can be treated similarly to resistors in parallel
3 see Q2
4 see Q2
5 capacitors in parallel can be treated in the same way as resistors in series.

I think it would be of more value to yourself if you read your notes, this is pretty basic stuff. If your still stuck, just go to wikipedia and read about capacitors.

 

[jenko]

im only 14 i shall look thank you for the help

 

[nhoj]

Hi jenko,

Old nick has given you the stuff you need to solve the probs. But familiarization about the units you are working with will be a a great help. You can understand what you are doing if you are familiar with the units of every parameters involved.

For example, watt is a unit of power not of energy. the unit of energy my be in joule. Also, the unit of charg is coulomb. Make sure to familiarize yourself with units before making your solutions. just a reminder =)

rgrds,
nhoj

 

[Old Nick]

2. i have been asked to find the 3rd value of a capacitor in series which will give the capacitence of 3 µf the two values are 10µf and 15µf

To get you started I'll show you haw to do this one.

(1/C1)+(1/C2)+(1/C3)= 1/Ccombined

thus

(1/10u)+(1/15u)+(1/X)= 1/3u

so, solving for X

(1/X)=1/3u-(1/10u)-(1/15u)

X=1/((1/3u)-(1/10u)-(1/15u))

X=6uF

 

[ilamseeker]

sorry dude...

 

[jenko]

hiya guys i have looks on wikipedia and im finding it raly difficult to work the energy and charge, i cannot get the grasp on how to work any of these questions out completely

IM STILL LOOKING ON THE WEB THOUGH!

CHEERS GUYS!

 

[Old Nick]

hiya guys i have looks on wikipedia and im finding it raly difficult to work the energy and charge, i cannot get the grasp on how to work any of these questions out completely

IM STILL LOOKING ON THE WEB THOUGH!

CHEERS GUYS!

I gave you the expression in my first reply!

If you google "energy in a capacitor", the first site it'll give you is this.

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/capeng.html

C=Q/V, where Q is the charge!!!

Everything you need is either on this thread or one google search away! You'll gain nothing by me giving you the answers. Knowledge and understanding and fought for and won, it can't be given.

Stick in, you'll get it eventually.

 

[jenko]

right ! ive done my home work bought a book with everything in it!
these are my final answers that i have i have used formulas but not going to write them as i havent the time readyy??!!!??

1. 6µf

2. equiviliant capacitence across series 25Πf
v1 500v
v2 250v
v3 166.7v
charge
c1 500Πc
c2 1000Πc
c3 1500Πc

3. ? working on ?

4. equivilant capacitence 50Πf
charge
c1 1200Πc
c2 1800Πc
c3 3000Πc

5.
80Πc
500Πc
1400Πc

113Πf across them all Cobination

6. 3.505Πf equivilant capacitence across the cobination in parrell and series

7. 8. 9. working on

10.

Added after 44 minutes:

any1?

 

[Old Nick]

your answers don't match your questions.

I gave you the answer and workings for question 2, and you seem to have it as the answer for question 1.

The rest of your answers don't seem to fit any question.

explain what this,

2. equiviliant capacitence across series 25Πf
v1 500v
v2 250v
v3 166.7v
charge
c1 500Πc
c2 1000Πc
c3 1500Πc

is all about and I'll have a shot at pointing out where you're going wrong and right.
And what is this symbol ' Π ' supposed to represent ??

 

[jenko]

nf = nano farads i think

 

[Old Nick]

nF = nano Farads

the F is capitalised.

Πc means nothing.

 

[jenko]

what unit should it be then ?:S

 

[Old Nick]

should what be?

I don't know what your numbers relate to.