A dipole of dipole moment $$\overrightarrow p $$ is placed in uniform electric field $$\overrightarrow E $$ then torque acting on it is given by

Electric field at centre O of semicircle of radius $$a$$ having linear charge density $$\lambda $$ given as

A charge Q is situated at the corner of a cube, the electric flux passed through all the six faces of the cube is