Two thin parallel threads carry a uniform charge with linear densities `lambda` and `-lambda` . The distance between the threads is equal to `l`. Find the potential of the electric field and the magnitude of its strength vector at the distance `r gt gt l` at the angle `theta` to the vector 1 (fig).

Answer

`(lambdalcostheta)/(2piepsi_(0)r),(lambdalcostheta)/(2piepsi_(0)r^(2))`