Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more. Why can insulators be charged by friction but not by conduction? Ask Question. Asked 6 years, 5 months ago. Active 5 years, 10 months ago.
Viewed 14k times. Improve this question. Add a comment. Active Oldest Votes. Improve this answer. Helder Velez Helder Velez 2, 17 17 silver badges 30 30 bronze badges. It is most noticeable when the layer is complete as is the case of the rare gas and that are very insulating. Since humidity levels tend to vary from day to day and season to season, it is expected that electrical effects and even the success of electrostatic demonstrations can vary from day to day.
Predicting the direction that electrons would move within a conducting material is a simple application of the two fundamental rules of charge interaction.
Opposites attract and likes repel. Suppose that some method is used to impart a negative charge to an object at a given location. At the location where the charge is imparted, there is an excess of electrons.
That is, the multitude of atoms in that region possess more electrons than protons. Of course, there are a number of electrons that could be thought of as being quite contented since there is an accompanying positively charged proton to satisfy their attraction for an opposite. However, the so-called excess electrons have a repulsive response to each other and would prefer more space.
Electrons, like human beings, wish to manipulate their surroundings in an effort to reduce repulsive effects. Since these excess electrons are present in a conductor, there is little hindrance to their ability to migrate to other parts of the object. And that is exactly what they do. In an effort to reduce the overall repulsive effects within the object, there is a mass migration of excess electrons throughout the entire surface of the object. Excess electrons migrate to distance themselves from their repulsive neighbors.
In this sense, it is said that excess negative charge distributes itself throughout the surface of the conductor. But what happens if the conductor acquires an excess of positive charge? What if electrons are removed from a conductor at a given location, giving the object an overall positive charge? If protons cannot move, then how can the excess of positive charge distribute itself across the surface of the material?
While the answers to these questions are not as obvious, it still involves a rather simple explanation that once again relies on the two fundamental rules of charge interaction. Suppose that a conducting metal sphere is charged on its left side and imparted an excess of positive charge.
Of course, this requires that electrons be removed from the object at the location of charging. A multitude of atoms in the region where the charging occurs have lost one or more electrons and have an excess of protons. The imbalance of charge within these atoms creates effects that can be thought of as disturbing the balance of charge within the entire object.
The presence of these excess protons in a given location draws electrons from other atoms. Electrons in other parts of the object can be thought of as being quite contented with the balance of charge that they are experiencing. Yet there will always be some electrons that will feel the attraction for the excess protons some distance away.
In human terms, we might say these electrons are drawn by curiosity or by the belief that the grass is greener on the other side of the fence. In the language of electrostatics, we simply assert that opposites attract - the excess protons and both the neighboring and distant electrons attract each other.
The protons cannot do anything about this attraction since they are bound within the nucleus of their own atoms. Yet, electrons are loosely bound within atoms; and being present in a conductor, they are free to move. These electrons make the move for the excess protons, leaving their own atoms with their own excess of positive charge.
This electron migration happens across the entire surface of the object, until the overall sum of repulsive effects between electrons across the whole surface of the object are minimized. Use your understanding of charge to answer the following questions. When finished, click the button to view the answers. One of these isolated charged spheres is copper and the other is rubber.
The diagram below depicts the distribution of excess negative charge over the surface of two spheres. Label which is which and support your answer with an explanation. See Answer Answer: A is rubber and B is copper. Sphere A shown a non-uniform distribution of excess charge; so sphere A must be made of an insulating material such as rubber.
The forces of attraction or repulsion are greater when the charged objects are closer. If a cloth rubs a plastic rod and the cloth is pulled away from the rod slightly, will the rod and cloth attract, repel or experience no force at all? The rod and cloth will attract. This is true as long as there is enough friction to transfer electrons. In both cases, the opposite charges will attract. Charging by friction When insulating materials rub against each other, they may become electrically charged.
Opposite charges attract. Like charges repel.
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