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My professor gave us the following reason:

The screen is positively charged. When dust particles fly near it, the positive charges in the screen induce a charge in the dust particle, pulling the negative charges closer to it, and pushing the positive charges away. The screen then attracts the negative side, pulling the dust particle to it.

But why does the screen attract the whole dust particle? Its only attracting the negative charges so why does the "whole" dust particle go to the screen? Why doesn't the screen just rip out the electrons, and repel away the rest of the particle?

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  • $\begingroup$ if your TV is an LCD then it's more likely that it just shows the dust more because it's a vaguely reflective surface (or you need to dust more often :p). I'm not certain about plasma I could believe they might elecrostatically attract dust. $\endgroup$ – Bowler Jan 9 '14 at 23:37
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Short answer:Finite size of dust particles and inverse square law.

The side of the dust particle towards the screen is negatively charged and the other side is positively charged.Now due to the inverse square law,the force of attraction is more than than the repulsion as the negative side is closer and the particle experiences a net force towards the screen.

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Why the electrons don't travel to the screen?

Because they still tightly held by the atoms of the dust particle.The T.V. screen only induced a slight polarization of the dust particle.The electrons have not travelled to the negative side(unlike conductors) but the atom itself undergoes slight polarization.(Similar to what happens in dielectrics).

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  • $\begingroup$ But why does it matter if they are being held tightly be the atoms of the dust particle? The pull by the screen is stronger (thats why the electrons broke free in the first place!) so why isn't it strong enough for the electrons to leave the boundary of the solid? (an arbitrary boundary) $\endgroup$ – dfg Jan 10 '14 at 14:10
  • $\begingroup$ The electron's didn't break off,each atom is just polarized,so it looks as if the there are actually free charges but there are not. $\endgroup$ – Sandesh Kalantre Jan 10 '14 at 14:19
  • $\begingroup$ But there thousands of atoms in a dust particle. If only the atoms are polarized, the entire particle wouldn't become polarized would it? $\endgroup$ – dfg Jan 14 '14 at 14:32
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When the electric charge on the dust particle is induced, it is attracted to the TV screen. The dust particle is a solid, the electric charge induced the TV screen, can (or not) move the particle (this depends on the particle itself), but the charge can't leave the solid structure of the particle and "float" in the air to the TV screen, because the amount of energy required to leave the solid is extremely high. Instead, the electrostatic force continues to act in such a way that attracts the whole particle. Furthermore, because the outside of the screen is made of glass, attracted charged particles can not compensate the charge of the screen (which is on the inside) because there is no electrical path in the glass, that is why remain attached to the screen.

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  • $\begingroup$ I still don't understand why the charges can't leave the solid and float to the to the TV. What force prevents it from leaving the solid? It can't be the electrostatic force from the nuclei because the electrons have already "broken free" from them. $\endgroup$ – dfg Jan 10 '14 at 1:35
  • $\begingroup$ And what exactly do you mean by "solid"? Isn't the solid just a bunch of atoms close together? Its not an entity in itself is it? $\endgroup$ – dfg Jan 10 '14 at 1:36
  • $\begingroup$ And why can't the electrons go through the screen? If the glass isn't a conductor there can't be current flow, but theres nothing stopping the electrons from just moving through the screen is there? $\endgroup$ – dfg Jan 10 '14 at 1:38
  • $\begingroup$ Not all solids have "free electrons". A solid is formed by a structure of atoms. Within this structure, there are shared electrons by the atoms, with a certain level energy. Increasing the energy level of those electrons, they become "free electrons" (within the structure of the solid). The "free electrons" are in the last level of energy of the solid. For these electrons leave the solid, the increase in energy required is extremely high, so they are bound to the atomic structure of the solid, and when subjected to electrostatic forces, they are attracted, "pulling" the solid. $\endgroup$ – Martin Petrei Jan 10 '14 at 9:55
  • $\begingroup$ The electric current is electron's flow. If the screen glass is an insulator, there can't be electric current through it, then the electrons can't pass through glass. $\endgroup$ – Martin Petrei Jan 10 '14 at 10:01
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Dust tends to remain suspended in air for long periods, which would imply that it is made of relatively light elements, carbon, sodium, silicates, etc. Most of these lighter elements apply a stronger force to their electrons, because they have less electron shells. This makes the force required to get them to shed electrons exponentially higher. Heavier elements like copper, zinc and lead give up electrons more easily, but wouldn't tend to stay suspended in air due to their greater mass.

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    $\begingroup$ So you're implying that the particles that stay suspended longer are more likely to stick to a TV screen? I don't really understand how the electronegativity part of your answer addresses the question. $\endgroup$ – Brandon Enright Mar 6 '15 at 16:58
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the positively charged particles attracted the negatively charged particles so when dust particles fly near the t.v. screen.the screen induces the charge in the dust particles pulling negatively charged particles closer to it.

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  • $\begingroup$ Two things you need to include in your answer: why the front of the TV is positively charged, and, why dust particles floating in your home are negatively charged. $\endgroup$ – Brandon Enright Mar 15 '15 at 7:33

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