Question

A charge of -7.00 nC is spread uniformly over the surface of one face of a nonconducting disk of radius 1.20 cm

Part A

Find the magnitude of the electric field this disk produces at a point P on the axis of the disk a distance of 3.00 cm from its center.

Part B

Suppose that the charge were all pushed away from the center and distributed uniformly on the outer rim of the disk. Find the magnitude of the electric field at point P.

Part C

If the charge is all brought to the center of the disk, find the magnitude and direction of the electric field at point P.

Part D

Why is the field in part (a) stronger than the field in part (b)?

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Part E

Why is the field in part (c) the strongest of the three fields?

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Answer 1

Part A The surface charge density is, 7x10 C π(0.012 m) 1.54x10-5 C/m2 The magnitude of the electric field at the point P is 2E Substitute the values in the above equation.

2E 1.54x10-5 2(8.85 x10 F/1.0 6.22 x104 NC Part B For the ring of the charge, the field is, Substitute the values in the above equation.

+a (9x10, N.m 2/C)(7x10-9 C)(0.03 m) (003m) +(0012 m 3.37x10- m -5.63x104 NC Part C For the point charge the magnitude of electric field is, kq E- 9x10° N m2 /C) (7x10 c) 0.03 m) -70000 N/C

Part D The effective distance of the point P in first case is more than in the second case. Part E The effective distance of point P is more in the case of rim than other two cases