In the figure, a solid sphere of radius a = 14.8 cm is concentric with a spheric

Question

In the figure, a solid sphere of radius a = 14.8 cm is concentric with a spherical conducting shell of inner radius b = 47.4 cm and outer radius c = 49.4 cm. The sphere has a net uniform charge q1 = 9.00×10-6C. The shell has a net charge q2 = -q1.
Find expressions for the electric field, as a function of the radius r, within the sphere and the shell (r < a). Evaluate for r = 7.4 cm.

Find expressions for the electric field, as a function of the radius r, between the sphere and the shell (a < r < b). Evaluate for r = 31.1 cm.

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Find expressions for the electric field, as a function of the radius r, inside the shell (b < r < c). Evaluate for r = 48.4 cm.

Find expressions for the electric field, as a function of the radius r, outside the shell (r > c). Evaluate for r = 50.4 cm.

What is the charge on the outer surface of the shell?

I know that these last three are all zero, but I am struggling to get the calculations correct for the first two parts.

Explanation / Answer

(a)
The charge enclosed by the Gaussian surface = q1(r/a)^3
4 * *r^2 *E = (q1/0) * (r/a)^3
E = (q1*r)/(4**0*a^3)

Substituing Values -
E = (9.0*10^-6 *0.074)/(4*3.14*8.85*10^-12*0.148^3)
E = 1.85 * 10^6 N/C

(b)
For r = 31.1 cm = 0.031 m
E * 4 * *r^2 = q/0
E = 1/4 * *0 * q/r^2
E = 8.9 * 10^9 * (9.0*10^-6)/(0.031)^2
E = 8.33 * 10^7 N/C

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