Problem 3.19

A very long uniformly charged thread oriented along the axis of a circle of radius $R$ rests on its centre with one of the ends. The charge of the thread per unit length is equal to $\lambda .$ Find the flux of the vector $\mathbf{E}$ across the circle area.

\text { | } \Phi \mid=1 / 2 \lambda R / \varepsilon_{0} \text { . The sign of \Phi depends on how the direction of the normal to the circle is chosen. }

Constant Electric Field in a Vacuum