# Cylinder capacitance question

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#1
Hi there

I posted this in maths, but think it might be more suitable here.

Please might anyone be able to advise me how to solve this problem in regard to the following cylinder? Dimensions L = 10-2 m, d = 10-3 m and D = 2 × 10-3 m.

I've been given the formula

Cm = (Capacitance/unit area ) x (surface area)

Calculate the capacitance of the outer curved surface if the material has:
Capacitance/surface area = 1.2 x 10-5 Fm2.
[Hint: circumference of a circle = 2pi x radius]

I'm not sure how to go about this. Should I multiply 1.2 x 10-5 Fm2 by 2 pi r h (the surface area of the outer curved surface) to answer the question?

Thank you very much
0
6 years ago
#2
Yes.
You need the total outer surface area of the cylinder. Then multiply it by the capacitance per unit area, which is given.
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#3
(Original post by Stonebridge)
Yes.
You need the total outer surface area of the cylinder. Then multiply it by the capacitance per unit area, which is given.
Thank you very much, Stonebridge!
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#4
(Original post by Stonebridge)
Yes.
You need the total outer surface area of the cylinder. Then multiply it by the capacitance per unit area, which is given.
Hi Stonebridge

Do you think I've calculated this correctly?

1.2 x 10-5 Fm2 x 2.pi.r.l = (1.2E-5) x (2)(pi)(1E-3)(10E-2) = 7.5E-9F

Thank you
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#5
(Original post by Ggdf)
Hi Stonebridge

Do you think I've calculated this correctly?

1.2 x 10-5 Fm2 x 2.pi.r.l = (1.2E-5) x (2)(pi)(1E-3)(10E-2) = 7.5E-9F

Thank you
I'm unsure because I did the calculation assuming that length represented height in 2.pi.r.h. so I therefore did 2.pi.r.l. Was this incorrect?

Thank you very much
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5 years ago
#6
The calculation is set up correctly but I get 10-10 at the end not 10-9

Is the length L =10-2m?

Just check the figures and the calculation.
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#7
(Original post by Stonebridge)
The calculation is set up correctly but I get 10-10 at the end not 10-9

Is the length L =10-2m?

Just check the figures and the calculation.

I've tried it again, but am still getting 10E-9. I'm not sure where I'm making a mistake.

The length is 10E-2m. I thought to calculate surface area by 2.pi.r.h, but then realised I have length not height.
0
5 years ago
#8
(Original post by Ggdf)

I've tried it again, but am still getting 10E-9. I'm not sure where I'm making a mistake.

The length is 10E-2m. I thought to calculate surface area by 2.pi.r.h, but then realised I have length not height.
It could be you are using the calculator incorrectly.

10-10 is entered as 1 exp -10 ( 1 x 10-10)
Are you sure you are not incorrectly entering 10 x 10-10?
This would give the incorrect 10-9
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#9
(Original post by Stonebridge)
It could be you are using the calculator incorrectly.

10-10 is entered as 1 exp -10 ( 1 x 10-10)
Are you sure you are not incorrectly entering 10 x 10-10?
This would give the incorrect 10-9

This is what I'm doing on the calculator:

I'm not sure where I'm going wrong.
0
5 years ago
#10
(Original post by Ggdf)

This is what I'm doing on the calculator:

I'm not sure where I'm going wrong.
It's the last term that's entered incorrectly.

10-2 is entered as 1 E -2 not 10 E-2

1 E -2 translates to 1 x 10-2
10 E -2 translates as 10 x 10-2

This is why you get 10-9 instead of 10-10

It's a common mistake in calculator usage.
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#11
(Original post by Stonebridge)
It's the last term that's entered incorrectly.

10-2 is entered as 1 E -2 not 10 E-2

1 E -2 translates to 1 x 10-2
10 E -2 translates as 10 x 10-2

This is why you get 10-9 instead of 10-10

It's a common mistake in calculator usage.
Thank you very much for pointing this out for me, I really appreciate it!
0
#12
(Original post by Stonebridge)
It's the last term that's entered incorrectly.

10-2 is entered as 1 E -2 not 10 E-2

1 E -2 translates to 1 x 10-2
10 E -2 translates as 10 x 10-2

This is why you get 10-9 instead of 10-10

It's a common mistake in calculator usage.

Hi Stonebridge

Sorry to bring this up again. I had a look at the last calculator photo, and it seems that I have entered 10E-2 rather than 1E-2. Is it definitely the final term that is entered incorrectly?

Thank you
0
5 years ago
#13
(Original post by Ggdf)
Hi Stonebridge

Sorry to bring this up again. I had a look at the last calculator photo, and it seems that I have entered 10E-2 rather than 1E-2. Is it definitely the final term that is entered incorrectly?

Thank you
Yes. The last term is entered incorrectly, as I said in my previous post.

If you have 10-2

you should enter it as

1 E -2
which means
1 x 10-2

If, as you have done, you enter

10 E -2
the calculator takes this as

10 x 10-2
0
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