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jpruim
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Member advised to use the homework template for posts in the homework sections of PF.
I've been given a copy of my friend's midterm exam from this same class from last term, and decided to take a crack at it to help study. One question type in particular really messes me up and it looks like the following. How would I go about solving these in the future?
A solid insulating sphere with radius A is at the center of a concentric conducting spherical shell of inner radius B and outer radius C. After the sphere and shell are charged, it is found that an electric field at a distance D from the center such that A < D < B is Q1 N/C radially inward, while the field at a distance G such that G > C is Q2 radially outward.
Find
1. The charge on the insulating sphere
2. The electric field at a radius such that r < A
3. The net charge on the hollow conducting sphere
4. The electric field at a radius such that B < r < C
5. The charges on the inner and outer surfaces of the hollow conducting sphereOn the assignment given, there were actual values for A-E, Q1 and Q2. However, I’ve replaced them with variables so that I can get more conceptual explanations.
My attempt at part 1 is as follows
[tex]q_e = \vec{E}\cdot 4 \pi r^2 \epsilon_0[/tex]
then set r = D, so that I get
[tex]q_e = \vec{E}\cdot 4 \pi D^2 \epsilon_0[/tex]
Note that D =/= A.
Thus, you would plug in the distance D where the electric field E is to be found, and this would tell me the charge on the insulating sphere (in theory) because the sphere is enclosed within a sphere of radius D.My attempt at part 2 is
[tex]\vec{E} = \frac{kQr}{R^3}[/tex]
where Q is the total charge (i.e. q_e found above), R is the sphere radius (R = A) and r is the electric field radius measurement.
Part 4 I know for sure is that it is 0 since r is within a conducting surface.However, I assume part 5 relies on part 3, which I have no idea how to calculate.
How would I go about solving part 3 and as well part 5? Are my answers for parts 1 and 2 correct?
A solid insulating sphere with radius A is at the center of a concentric conducting spherical shell of inner radius B and outer radius C. After the sphere and shell are charged, it is found that an electric field at a distance D from the center such that A < D < B is Q1 N/C radially inward, while the field at a distance G such that G > C is Q2 radially outward.
Find
1. The charge on the insulating sphere
2. The electric field at a radius such that r < A
3. The net charge on the hollow conducting sphere
4. The electric field at a radius such that B < r < C
5. The charges on the inner and outer surfaces of the hollow conducting sphereOn the assignment given, there were actual values for A-E, Q1 and Q2. However, I’ve replaced them with variables so that I can get more conceptual explanations.
My attempt at part 1 is as follows
[tex]q_e = \vec{E}\cdot 4 \pi r^2 \epsilon_0[/tex]
then set r = D, so that I get
[tex]q_e = \vec{E}\cdot 4 \pi D^2 \epsilon_0[/tex]
Note that D =/= A.
Thus, you would plug in the distance D where the electric field E is to be found, and this would tell me the charge on the insulating sphere (in theory) because the sphere is enclosed within a sphere of radius D.My attempt at part 2 is
[tex]\vec{E} = \frac{kQr}{R^3}[/tex]
where Q is the total charge (i.e. q_e found above), R is the sphere radius (R = A) and r is the electric field radius measurement.
Part 4 I know for sure is that it is 0 since r is within a conducting surface.However, I assume part 5 relies on part 3, which I have no idea how to calculate.
How would I go about solving part 3 and as well part 5? Are my answers for parts 1 and 2 correct?