18. Two identical thin rods of length \( 2 a \) carry equal charges \( + Q \) that is distributed uniformly along their lengths. The rods lie along the \( x \)-axis with their centers separated by a distance \( b>2 a \). Then the magnitude of the force exerted by the left rod on the right one is given by " \( \frac{Q^{2}}{16 \pi \varepsilon_{0} a^{2}} \log _{e}\left(\frac{b^{2}}{b^{2}-N a^{2}}\right) \) ". Find the value of "N"

Question

18. Two identical thin rods of length \( 2 a \) carry equal charges \( + Q \) that is distributed uniformly along their lengths. The rods lie along the \( x \)-axis with their centers separated by a distance \( b>2 a \). Then the magnitude of the force exerted by the left rod on the right one is given by " \( \frac{Q^{2}}{16 \pi \varepsilon_{0} a^{2}} \log _{e}\left(\frac{b^{2}}{b^{2}-N a^{2}}\right) \) ". Find the value of "N"