# Gauss Law use in an example question

In the textbook (Modern Physics for Scientists and Engineers by Douglas Giancoli) it asks for a capacitance calculation. However, I want just the explanation of the electric field calculation between two concentric cylinders. Why does he ignore the outer cylinder and write the electric field only due to the inner one?

• What is the electric field due to the outer cylinder at distance $<R_a$? (Hint: use Gauss' law) May 21, 2017 at 22:35
• @ShaVuklia Oops, yes definitely it is 0 due to the oiter cylindre. Sorry for the stupidity:( May 21, 2017 at 22:40
• No worries, it was a good question! It shows you were reading the text critically - and that's good! May 21, 2017 at 23:09
• Please don't post questions that consist of cell phone pictures from a book: physics.meta.stackexchange.com/q/10563 . This severely limits the usefulness of the question, e.g., by making it not searchable in search engines and making it inaccessible to visually impaired people. Also, I'll add the homework-and-exercises tag, but in the future please use that tag on questions of this type.
– user4552
May 27, 2018 at 18:39

$\Phi_{E} = \frac{q_{in}}{\epsilon_{0}}$