A thin, nonconducting rod of length \(L\) lies along the \(x\)-axis with its left end at the origin \(x = 0\) and its right end at \(x = L\). The rod carries a non-uniform linear charge density given by \(\lambda(x) = \alpha x\), where \(\alpha\) is a positive constant with appropriate units. Which of the following expressions gives the magnitude of the electric field at a point \(P\) on the \(x\)-axis located at \(x = d\), where \(d > L\)?