An infinite long semicircular tube is given as shown below one half is given a surface charge density $+\sigma$ and other half is given charge density $-,\sigma$ . Electric field at a point on axis would be

Question

 

$(A)\;\frac {\sigma}{\pi \in _0} \hat j \\ (B)\;\frac {\sigma}{\pi \in _0} \hat i \\ (C)\; \frac {-\sigma}{\pi \in _0} \hat i \\ (D)\;\frac {\sigma}{\pi \in _0} \hat j$