A thin plastic spherical shell of radius 5 cm has a uniformly distributed charge

Question

A thin plastic spherical shell of radius 5 cm has a uniformly distributed charge of -30 nC on its outer surface. A concentric thin plastic spherical shell of radius 8 cm has a uniformly distributed charge of +66 nC on its outer surface. Find the magnitude and direction of the electric field at distances of 3 cm, 7 cm, and 10 cm from the center. See the figure.

(a) 3 cm Correct: Your answer is correct. N/C Correct: Your answer is correct.

(b) 7 cm _____N/C Correct: Your answer is correct.

(c) 10 cm _____N/C Correct: Your answer is correct.

Explanation / Answer

r1 = 5 cm ; q1 = -30 nC ; r2 = 8 cm ; q2 = +66 nC

a)3 cm

At 3 cm, E = 0 ; since the field inside the conductor is always zero.

b)r = 7 cm = 0.07 m

E = k q1/ r^2

E = 9 x 10^9 x 30 x 10^-9 / 0.07^2 = 5.5 x 10^4 N/C

HEnce, E = 5.5 x 10^4 N/C

c)r = 10 cm = 0.1 m

q = q1+q2 = -30 + 66 = 36 nC

E = 9 x 10^9 x 36 x 10^-9/0.1^2 = 3.24 x 10^4 N/C

Hence, E = 3.24 x 10^4 N/C

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