When you rub a balloon on a sweater, you create a static electric charge through a process called triboelectric charging, where electrons are transferred from the sweater to the balloon. As a result, the balloon becomes negatively charged due to the excess of electrons, while the sweater becomes positively charged because it has lost some of its electrons.
When you bring the negatively charged balloon close to a neutral wall, a couple of things happen:
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Induction: The presence of the negatively charged balloon will repel the negative charges (electrons) in the wall, causing them to move away from the side closest to the balloon. Meanwhile, the positive charges (which are the atomic nuclei) in the wall remain relatively fixed. This creates a region of positive charge on the surface of the wall that is closest to the balloon. The positive charge is not actually moving; instead, it is a result of the repulsion of the negative charges.
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Attraction: Even though the balloon is negatively charged, the positively induced surface on the wall will create an attractive force between the balloon and the wall.
Comparison of Movement:
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Negative Charges: The movement of negative charges (electrons) is dynamic; they can move relatively freely through conductive materials or be influenced to redistribute in insulating materials under the influence of external electric fields (like the one created by the balloon).
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Positive Charges: The positive charges (nuclei) do not move in the same way; they are fixed in place within the atoms of the material. What changes are the distributions of the electrons around them.
Explanation:
The key difference in movement arises from the nature of charge carriers. Electrons are lighter and more mobile compared to positive charges (which are part of atomic nuclei and remain fixed in place). When an external electric field (from the negatively charged balloon) is applied, it affects how electrons move around. This leads to the observable effects of attraction and repulsion when charged objects are near each other.
In summary, the balloon induces polarization in the wall; the redistribution of electrons creates a surface that allows the balloon to be attracted to the wall due to the positive charges remaining relatively stationary and attracted to the negatively charged balloon.