Hi there!
We can begin by using Coulomb's Law:
[tex]E = \frac{kq}{r^2}[/tex]
k = Coulomb's Constant (8.99 × 10⁹ Nm²/C²)
E = Electric field strength (N/C)
r = distance from point (m)
q = charge (C)
Since this is a continuous charge, we must use calculus.
We can express this as the following:
[tex]q = \lambda L[/tex]
λ = Linear charge density (C/m)
L = Length of rod (m)
Now, since this is an arc, L = s (arc length). Additionally, we must find the differential elements of each:
[tex]dq = \lambda ds\\\\dq = \lambda rd\theta[/tex]
Our new equation is:
[tex]dE = \frac{kdq}{r^2}\\\\dE = \frac{k\lambda rd\theta}{r^2}[/tex]
However, we will only take the cosine component of the electric field since the vertical components will cancel out. (Electric fields are a vector). Therefore:
[tex]dE = \frac{k\lambda rd\theta}{r^2}cos\theta\\\\dE = \frac{k\lambda}{r}cos\theta d\theta[/tex]
Integrate. For a semicircle, the bounds will be from -π/2 to π/2.
[tex]E = \frac{k\lambda}{r}\int\limits^{\frac{\pi}{2}}_{-\frac{\pi}{2}}} {cos\theta} \, d\theta\\\\E = \frac{k\lambda}{r}sin\theta\left \|{\frac{\pi}{2}} \atop {-\frac{\pi}{2}}} \right. \\\\E = \frac{k\lambda}{r}(1 - (-1)) = \frac{2k\lambda}{r}[/tex]
We need to solve for λ, which is Q/ L:
[tex]\lambda = \frac{3.10 \times 10^{-9} C}{\pi (0.05)} = 1.9735 \times 10^{-8} \frac{C}{m}[/tex]
Now, plug and solve for the electric field strength:
[tex]E = \frac{2(8.99\times 10^9)(1.9735\times 10^{-8})}{0.05} = \boxed{7096.783 \frac{N}{C}}[/tex]
**A diagram was not provided, but if the hemisphere's focus was to the right, the electric field would be to the right, and etcetera.
