State Gauss's theorem in electrostatiics. State the expression for electric field intensity at a point outside an infinitely long charged conducting cylinder.

Explanation

### Step-by-Step Solution

**Step 1: State Gauss's Theorem in Electrostatics**

Gauss's theorem, also known as Gauss's law, states that the total electric flux (\( \Phi_E \)) through a closed surface is equal to the total charge (\( Q \)) enclosed by that surface divided by the permittivity of free space (\( \epsilon_0 \)). Mathematically, it can be expressed as:

\[
\Phi_E = \oint \vec{E} \cdot d\vec{A} = \frac{Q}{\epsilon_0}
...