question_answer

Two electric dipoles of moment P and 64 P are placed in opposite direction on a line at a distance of 25 cm. The electric field will be zero at point between the dipoles whose distance from the dipole of moment P is [MP PET 2003]

A)            5 cm

B)                                      \[\frac{25}{9}\]cm

C)            10 cm                                      

D)            \[\frac{4}{13}\] cm

Correct Answer: A

Solution :

           Suppose neutral point N lies at a distance x from dipole of moment p or at a distance x2 from dipole of 64 p. At N |E. F. due to dipole |= |E. F. due to dipole ‚| Þ \[\frac{1}{4\pi {{\varepsilon }_{0}}}.\frac{2p}{{{x}^{3}}}=\frac{1}{4\pi {{\varepsilon }_{0}}}.\frac{2(64p)}{{{(25-x)}^{3}}}\] Þ \[\frac{1}{{{x}^{3}}}=\frac{64}{{{(25-x)}^{3}}}\] Þ x = 5 cm.