# Coulomb's law and Electric field intensity problem

1. Oct 31, 2015

### rizwanibn

I am not getting the answer to this question as shown in the text book.
Please help...!

My attempt is in the last attachment.

Thanks.!

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• ###### 1446272683526.jpg
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2. Oct 31, 2015

### blue_leaf77

Be carefull with the absolute sign in the inequality. $0.1 \leq |x| \leq 0.2 = (x\leq -0.1 \cup x\geq 0.1) \cap -0.2\leq x \leq 0.2$.

3. Nov 2, 2015

### rizwanibn

New attachment

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4. Nov 2, 2015

### rizwanibn

New attachment

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5. Nov 3, 2015

### blue_leaf77

Yes, I think that should give you the correct answer.

6. Nov 3, 2015

### rizwanibn

Is it addition of subtraction in between...?

7. Nov 3, 2015

### blue_leaf77

On a second thought, I think your the integration volume should be eight small cubes of sides 0.1 at each corner of a large cube of sides 0.4. As illustration for x-y plane, see picture below. The intersection area in that picture actually forms four long bar of square cross section when put in a 3D coordinate. If you add the last region corresponding to the inequality for $z$, you should get 8 cubes as the integration volume.

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• ###### Volumes.png
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Last edited: Nov 3, 2015
8. Nov 3, 2015

### rizwanibn

Thanks very much.
Got a very good understanding of it.
So all the cubes has a pair of opposite sign and they cancel out each other.

9. Nov 4, 2015

### blue_leaf77

You have to do the calculation to see if that's true.

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