The total electric field at a point on the axis of a uniformly charged disk, which has a radius R and a uniform charge density of σ, is given by the following expression, where x is the distance of the point from the disk. Ex = 2πkeσ 1 − x (R2 + x2)1/2 Consider a disk of radius R = 2.91 cm having a uniformly distributed charge of +5.18 μC. (a) Using the expression above, compute the electric field at a point on the axis and 2.79 mm from the center. N/C (b) Explain how the answer to part (a) compares with the field computed from the near-field approximation E = σ/2ε0. (c) Using the first expression above, compute the electric field at a point on the axis and 27.9 cm from the center of the disk. N/C (d) Explain how the answer to part (c) compares with the electric field obtained by treating the disk as a +5.18-μC charged particle at a distance of 27.9 cm.