Find the magnitude and direction of electric field at point $P$ in Fig. 1.53.

 

Figure 1.54 shows four point charges at the corners of a square of side $2 \mathrm{cm}$. Find the magnitude and direction of the electric field at the centre $O$ of the square, if $Q=0.02 \mu \mathrm{C}$

Use $\frac{1}{4\pi {\epsilon }_0}=9\times {10}^9{\mathrm{Nm}}^2{\mathrm{C}}^{-2}$