A curve segment $L,$ defined by the equations $z=0,x^2+y^2=a^2,$ and $x,$yin$[0,a],a>0,$ is located in space. This curve segment carries a total charge $Q$ uniformly distributed along it$.$

a$)$ Write the explicit expression for the volume charge density $$ corresponding to this charge distribution.

b$)$ Calculate the electric field $E$ at the point $P(0,0,0).$

c$)$ Compute separately the force exerted on a point charge $q,$ placed at $P(0,0,0),$ by the total charge $Q$ on the curve segment $L,$ and the force exerted by the point charge $q$ on the charge $Q$ distribute

$$ekil$-1$d along the curve $L.$ Discuss the results.