A conducting sphere is placed within a conducting spherical shell as shown in th

Question

A conducting sphere is placed within a conducting spherical shell as shown in the figure below. The conductors are in electrostatic equilibrium. The inner sphere has a radius of 1.50 cm, the inner radius of the spherical shell is 2.25 cm, and the outer radius of the shell is 2.75 cm. The inner sphere has a charge of 285 nC, and the spherical shell has zero net charge.

(a) What is the magnitude of the electric field at a point 1.75 cm from the center?
=?? N/C

(b) What is the electric field magnitude at a point 2.50 cm from the center? [Hint: What must be true about the electric field inside a conductor in electrostatic equilibrium?]
=?? N/C

(c) What is the electric field magnitude at a point 3.20 cm from the center?
=?? N/C

Explanation / Answer

1)The electric field between the sphere and the shell is the
same as if you placed a point charge in the middle of the
sphere with the same charge as the shell itself, (235 nC in
your example.)
So:
E=(k*q)/(r^2)
is your equation and your answer should
be in units of N/C. Remember to convert your nC to
Coulombs, and your cm to meters before doing the
calculation.

2)The electric field within any conducting material is zero if it
is in electrostatic equilibrium (zero net charge.) Since all
points at 2.50 cm from the center are within that shell, the
electric field is also zero.

3) Same equation as 1, you are just changing the distance
(r) from 0.0150 m to 0.0280 m.

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