A thin plastic bowl is exactly half of a sphere of radius $5.0\ \text{cm}$. Its curved surface carries a charge of $+2.0\ \text{nC}$, spread evenly over it. The point $C$ is the centre of the flat circle of its rim, which is also the centre of the sphere, as in the figure. The bowl is far from other charges. Take $\dfrac{1}{4\pi\varepsilon_0} = 9.0 \times 10^{9}\ \text{N m}^2\,\text{C}^{-2}$. Every bit of the charge is the same distance from $C$. What is the size of the electric field at $C$?

Fig. 1: A cross-section of a thin bowl that is half of a sphere of radius 5.0 cm, open at the top. Plus signs along the curved surface show its charge of plus 2.0 nanocoulombs. A dashed line joins the two ends of the rim, and the point C at its middle is the centre of the sphere. A radius from C to the bowl is labelled 5.0 cm.