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Some theoretical questions that got me confused during physics lecture today.

  1. bringing a conducting balloon to a negatively charged rod close will allow the conducting balloon have positive charges closer to the rod. when the rod touches the conducting balloon, why is it that the rod(dielectric) transfers its -ve charges to the conductor instead of other way around since it's harder for charges to move inside a dielectric.

  2. How exactly does charge by friction work? How I recognize it is that the stronger insulator will absorb electrons from the weaker insulator leaving one positively charged and one negatively charged?

  3. When you charge a balloon and stick it to a wall, after sometime the balloon slowly loses its charged state. But balloon is a dielectric(rubber) so how does it lose the charge? I'm assuming friction from rubbing against air slowly picks away at the charged electrons? Some clearer explanation would be great!

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  • $\begingroup$ Please read up on the triboelectric effect $\endgroup$ – QuIcKmAtHs Jan 10 '18 at 5:45
  • $\begingroup$ @XcoderX I've already read that. That also only answers 1 of my questions. $\endgroup$ – Justin Li Jan 10 '18 at 5:54
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Adhesion between different materials can result in a transfer of electrons between the two materials.
This is the reason for bodies gaining net charges after they have been in contact with one another - charging by friction.
Different substances have different affinities for electrons but to predict which substance will gain/lose electrons is very difficult and it is the empirical results which are usually quoted as a triboelectric table.

Your balloon although a good insulator in the bulk might have surface moisture on its surface and as water is a relatively good conductor in electrostatics experiments some of the charge might leak away by conduction through the water.

Although the air is a good insulator there are charged particles (ions and electrons) in the air which may originate from dust, air blown over a wet surface, hot bodies/flames, natural radioactivity and cosmic rays. These charges in the air will neutralise the charges which are on the balloon.
Feynman has a chapter in his book entitled Electricity in the Atmosphere which will give you some more information.

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  • $\begingroup$ I see. That most of the things up, thanks! But I'm still confused on why a conducting balloon is able to 'steal' charges from a -ve charged glass rod? $\endgroup$ – Justin Li Jan 10 '18 at 15:21
  • $\begingroup$ It will do it by contact with the glass rod which will not be a very efficient process. Transfer might be improved by rolling the glass rod over the balloon? $\endgroup$ – Farcher Jan 10 '18 at 16:23
  • $\begingroup$ Hmm I don't think that was 100% what I meant. What I meant was, why is it that the conductor is able to take charges from the insulator? The insulator disallows movements within it while a conductor lets electrons move freely. So isn't it easier for insulator to take parts of the -ve charges instead of conductor taking charges from the insulator? $\endgroup$ – Justin Li Jan 10 '18 at 16:42

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