# Find the charge on the outer surface

#### Fatima Hasan

1. Homework Statement

2. Homework Equations
$E=\frac{kQ}{r^2}$

3. The Attempt at a Solution

The answer is "A".Right ?

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#### BvU

Science Advisor
Homework Helper
Hello Fatima,

PF is not intended for stamp-approvals. If you convince yourself that -9 nC is the right answer, then that IS your answer for this exercise !

And why shouldn't it be the right answer ?

Science Advisor
Homework Helper
Yeah, well...

#### Fatima Hasan

Hello Fatima,

PF is not intended for stamp-approvals. If you convince yourself that -9 nC is the right answer, then that IS your answer for this exercise !

And why shouldn't it be the right answer ?
I was not pretty sure. Just wanted to confirm my answer. Sorry for multiple questions but my exam is after hours. I wish I have not broken the forum rules. Thanks

Last edited:

#### BvU

Science Advisor
Homework Helper
Best of luck for your test!

#### ehild

Homework Helper
1. Homework Statement
View attachment 223911

2. Homework Equations
$E=\frac{kQ}{r^2}$

3. The Attempt at a Solution
View attachment 223912
The answer is "A".Right ?
You wrote that Q=1 nC and then that Q=-10+1 =-9 nC. These are wrong, although the answer "A" is correct. Pay more attention!

BvU

#### Fatima Hasan

You wrote that Q=1 nC and then that Q=-10+1 =-9 nC. These are wrong, although the answer "A" is correct. Pay more attention!
$Q_0=-10+1=-9nC$

#### ehild

Homework Helper
$Q_0=-10+1=-9nC$
-10+1 is not -9 nC . Write out the units at both sides of an equation.

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