The electric field along the axis of a uniformly charged disk of radius R and total charge Q was calculated in Example 23.9. Show that the electric field at distances x that are large compared with R approaches that of a particle with charge Q 5 spR2. Suggestion: First show that x/(x 2 1 R2)1/2 5 (1 1 R2/x 2)21/2 and use the binomial expansion (1 1 d)n < 1 1 nd, when d ,, 1.