In this question, I am confusing with conducting and insulating shell concept. I

Question

In this question, I am confusing with conducting and insulating shell concept. I am wondering the key differences between the shells which are conducting and insulating. If somebody can explain clearly "The differences between conducting and insulating shells and their charge distributions according to those." I will be happy. Thanks!

- The correct answer for the 14th question is "B", but I selected "A" which is the wrong answer. I thought like conducting shell's inside should be (-5q) and outside is (+5q).

Questions 13 and 14 The figure below shows a solid insulating sphere that is concentric with a conducting spherical shell. The inner solid sphere carries a charge of +5 C uniformly distributed throughout its volume and the outer shell carries a net charge of-7 C. No other charges are present. The radii shown have the values R1-10 cm, R2-20 cm. and R3 30 cm. 13. Find the magnitude and direction of the electric field at a radial distance of = 50 cm from the center A. B. C. D. E. 72000 N/C; radially outward 36000 N/C; radially inward 96000 N/C; radially outward 72000 N/C; radially inward 36000 N/C; radially outward 14. Determine the charge distribution on the conducting shell A. B. C. D. E, inner surface:-5 C; outer surface: +2 C inner surface: -5 HC; outer surface: -2 HC inner surface:-7 C; outer surface: zero inner surface: zero, outer surface:-7 C inner surface: +5 C; outer surface :-7 C

Explanation / Answer

two points to be noted for condcting shell are

1. in conducting shell, charge can move from one part to another part but in insulating shell this in not possible and charge cannot move.

2. charge cannot reside inside the conductor and always reside on the surface but in case of insulating charge can be inside.

3. elelctric filed inside the condutor is zero but that not a necessity in insuators.

now coming to the question 14

using point 3 stated above, the charge on innner surface must be -5micro coulomb so that net electric field inside the conducting shell is zero.

now -7 micro coulomb charge already present on outer surface and due to charge -5micro coulomb on inner surface there will be +5micro coulomb extra charge on outer surface just . these -5micro coulomb and+5micro coulomb cherges on conducting shell are due to separation of electron from atom of leaving behing positive charge on atom.

now total charge on outer surface = -7 + 5 = -2 micro coulomb

so option B correct

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