Four charges are placed on corners of a square as shown in figure having side of 5 cm. If Q is one microcoulomb, then electric field intensity at centre will be

Side a=5×10−2mHalf of the diagonal of the square r=a2Electric field at centre due to charge q E=kqa22Now field at O=E2+E2=E2=kqa22⋅2=9×109×10−6×2×25×10−22=1.02×107N/C (upward)