# Cylinder capacitance question

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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)

And have been asked to answer this question:

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?

Please might anyone be able to advise me?

Thank you very much

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)

And have been asked to answer this question:

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?

Please might anyone be able to advise me?

Thank you very much

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#2

Yes.

You need the total outer surface area of the cylinder. Then multiply it by the capacitance per unit area, which is given.

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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(Original post by

Yes.

You need the total outer surface area of the cylinder. Then multiply it by the capacitance per unit area, which is given.

**Stonebridge**)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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**Stonebridge**)

Yes.

You need the total outer surface area of the cylinder. Then multiply it by the capacitance per unit area, which is given.

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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(Original post by

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

**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

Thank you very much

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#6

The calculation is set up correctly but I get 10

Is the length L =10

Just check the figures and the calculation.

^{-10}at the end not 10^{-9}Is the length L =10

^{-2}m?Just check the figures and the calculation.

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(Original post by

The calculation is set up correctly but I get 10

Is the length L =10

Just check the figures and the calculation.

**Stonebridge**)The calculation is set up correctly but I get 10

^{-10}at the end not 10^{-9}Is the length L =10

^{-2}m?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.

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#8

(Original post by

Thank you for your reply.

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.

**Ggdf**)Thank you for your reply.

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.

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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(Original post by

It could be you are using the calculator incorrectly.

10

Are you sure you are not incorrectly entering 10 x 10-10?

This would give the incorrect 10

**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.

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#10

(Original post by

Thank you for your help.

This is what I'm doing on the calculator:

I'm not sure where I'm going wrong.

**Ggdf**)Thank you for your help.

This is what I'm doing on the calculator:

I'm not sure where I'm going wrong.

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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(Original post by

It's the last term that's entered incorrectly.

10

1 E -2 translates to 1 x 10

10 E -2 translates as 10 x 10

This is why you get 10

It's a common mistake in calculator usage.

**Stonebridge**)It's the last term that's entered incorrectly.

10

^{-2}is entered as 1 E -2 not 10 E-21 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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**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

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#13

(Original post by

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

**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

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}

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