A \( + 3{\text{ C}}\) charge and a \( - 4{\text{ C}}\) charge are a distance \(x\) apart. P is a distance \(x\) from the \( + 3{\text{ C}}\) charge on the straight line joining the charges.

What is the magnitude of the electric field strength at P?

A.     \(\frac{1}{{\pi {\varepsilon _0}{x^2}}}\)

B.     \(\frac{1}{{2\pi {\varepsilon _0}{x^2}}}\)

C.     \(\frac{1}{{4\pi {\varepsilon _0}{x^2}}}\)

D.     \(\frac{1}{{7\pi {\varepsilon _0}{x^2}}}\)

B

Although it is convenient to use k in the equation for coulombic attraction, candidates need to be able to unpack this as \(\frac{1}{{4\pi {\varepsilon _0}}}\).