conceptual doubts in electrostatics

well i will tr to answer these!

1)

the rod is charged...say it has positive charge...

then....

what it does is, when it finds paper nearby, which was initially electrically neutral, it induces a negative charge in the nearer part and positive charge in the farther end...

as a result there is a net attractive force on the paper and it is attracted

but when the paper comes in contact with the charged rod, a bit of positive charge flows into the paper...and so the paper as a whole becomes a positively charged entity and it gets repelled by the positively charged rod!

i know that 2 positively charged bodies CAN attract each other at times, but i am igoring that case in this level until the question is raised! :P

3)

Tilll the time the electrons remain in the metals, there is no net charge developed in the metal...

now as soon as an electron leaves the metal surface, a positive charge will appear in the metal which will attract the electron and thus there will be creation of potential energy in the system

but as we know energy cannot get created from no-where and is conserved, the case of an electron dumping the metal for something else is out of question until we provide energy from outside to it

and when the energy provided is in the form of light the process of electron release is called photoelectric effect

when electrons are released due to application of heat, it is called thermionic emmission!

2) for this question i have different views..

invariably the force is not purely gravitational

but the force is resultant of all the interactive forces possible

like electrostatic gravitational magnetic and shayad many more abt which I/We are unaware of! :)

but the thing is gravitational force for the system is more than the other forces and it predominates and thus we consider only forces of gravitation!