# 查看完整版本 : [向CHING 求救!!!]關於electrostatic既MC!!!!

dicky821 2012-7-12 01:57 PM

## [向CHING 求救!!!]關於electrostatic既MC!!!!

Earth 左X之後, X會變成positive, 但X同Y係in contact, 之後再separate, 咁唔會都share左D positive charge 比Y, 令到2個變成positive?
[img]http://i1126.photobucket.com/albums/l617/dicky821/ph3-1.jpg[/img]

[img]http://i1126.photobucket.com/albums/l617/dicky821/ph4.png[/img]

[img]http://i1126.photobucket.com/albums/l617/dicky821/PH3.jpg[/img]

hk56740 2012-7-12 04:24 PM

1.留意字眼,個rod冇話拎走, +ve charges are still attracted towards the rod,sphere Y is uncharged,ans=D

2.metal spheres are good conductors of electricity. -ve charges are attracted towards the rod and +ve charges are repelled away,so ans=C

3.+ve charges are attracted towards the rod and -ve charges are repelled away to the end of sphere Z. electrostatic attractive force between electrons on rod and positive charges on sphere X is stronger than the electrostatic repulsive force between electrons on rod and electrons on sphere Z(since F is inversely proportional to the square of distance), electrons on sphere Z are earthed away.As the rod is still near the sphere X, positive charges are still attracted,so ans=A

[[i] 本帖最後由 hk56740 於 2012-7-12 04:25 PM 編輯 [/i]]

Ron~ 2012-7-12 04:49 PM

1991/II/29
Should be D
When X is earthed, electrons(negative charges) flow though your finger to the earth, causing Y carries zero charge.
Between rod C and sphere X, the attracted force is to large so that the positive charges remain at the left of sphere X.
1995/II/29
C
1998/II/29
A
Again, when Y is earthed, electrons(negative charges) flow away(to the earth), resulting positive charges remain at the left of sphere X.
When you treat X, Y and Z as one conductor(as they are touched in contact), only positive charges remain when earthed.

[[i] 本帖最後由 Ron~ 於 2012-7-12 04:50 PM 編輯 [/i]]