Can insulators have a charge

If you run a plastic comb through your hair, the charged comb can pick up neutral pieces of paper. When a charged rod is brought near a neutral substance, an insulator in this case, the distribution of charge in atoms and molecules is shifted slightly.

Opposite charge is attracted nearer the external charged rod, while like charge is repelled. Since the electrostatic force decreases with distance, the repulsion of like charges is weaker than the attraction of unlike charges, and so there is a net attraction. Thus, a positively charged glass rod attracts neutral pieces of paper, as will a negatively charged rubber rod. Some molecules, like water, are polar molecules.

Polar molecules have a natural or inherent separation of charge, although they are neutral overall. Polar molecules are particularly affected by other charged objects and show greater polarization effects than molecules with naturally uniform charge distributions. When the two ends of a dipole can be separated, this method of charging by induction may be used to create charged objects without transferring charge. In Figure 1.

A positively charged rod is brought near one of them, attracting negative charge to that side, leaving the other sphere positively charged. Another method of charging by induction is shown in Figure 1. The neutral metal sphere is polarized when a charged rod is brought near it.

The sphere is then grounded, meaning that a conducting wire is run from the sphere to the ground. Since Earth is large and most of the ground is a good conductor, it can supply or accept excess charge easily. In this case, electrons are attracted to the sphere through a wire called the ground wire, because it supplies a conducting path to the ground.

Note that the extra positive charges reside on the surface of the glass rod as a result of rubbing it with silk before starting the experiment. Since only electrons move in metals, we see that they are attracted to the top of the electroscope.

There, some are transferred to the positive rod by touch, leaving the electroscope with a net positive charge. Figure 2. An electroscope is a favorite instrument in physics demonstrations and student laboratories. It is typically made with gold foil leaves hung from a conducting metal stem and is insulated from the room air in a glass-walled container. Like charges in the light flexible gold leaves repel, separating them.

Electrostatic repulsion in the leaves of the charged electroscope separates them. The electrostatic force has a horizontal component that results in the leaves moving apart as well as a vertical component that is balanced by the gravitational force. Similarly, the electroscope can be negatively charged by contact with a negatively charged object. It is not necessary to transfer excess charge directly to an object in order to charge it.

Figure 3 shows a method of induction wherein a charge is created in a nearby object, without direct contact. Here we see two neutral metal spheres in contact with one another but insulated from the rest of the world. A positively charged rod is brought near one of them, attracting negative charge to that side, leaving the other sphere positively charged.

This is an example of induced polarization of neutral objects. Polarization is the separation of charges in an object that remains neutral. If the spheres are now separated before the rod is pulled away , each sphere will have a net charge. Note that the object closest to the charged rod receives an opposite charge when charged by induction. Note also that no charge is removed from the charged rod, so that this process can be repeated without depleting the supply of excess charge.

Figure 3. Charging by induction. Another method of charging by induction is shown in Figure 4. The neutral metal sphere is polarized when a charged rod is brought near it.

The sphere is then grounded, meaning that a conducting wire is run from the sphere to the ground. Since the earth is large and most ground is a good conductor, it can supply or accept excess charge easily. In this case, electrons are attracted to the sphere through a wire called the ground wire, because it supplies a conducting path to the ground.

The ground connection is broken before the charged rod is removed, leaving the sphere with an excess charge opposite to that of the rod. Again, an opposite charge is achieved when charging by induction and the charged rod loses none of its excess charge.

Figure 4. Charging by induction, using a ground connection. Neutral objects can be attracted to any charged object. The pieces of straw attracted to polished amber are neutral, for example. 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.

Sphere B shows a uniform distribution of excess charge; one would reason that it is made of a conductor such as copper. Which of the following materials are likely to exhibit more conductive properties than insulating properties?

Aluminum and silver are metals, making them good conductors. The human body is a fairly good conductor. When wet, its an even better conductor. A and B are characteristic of positive and negative objects.

As for C, both insulators and conductors can be charged. As for D, this has nothing to do with the conductive properties of materials. As for E, neutrons are located in the nucleus and are "out of the way" of mobile electrons. Suppose that a conducting sphere is charged positively by some method. The charge is initially deposited on the left side of the sphere. Yet because the object is conductive, the charge spreads uniformly throughout the surface of the sphere.

Rule out A since atoms are not capable of moving within solid spheres. Rule out B since protons are not capable of moving in electrostatic demos. C is the proper explanation since the negative electrons are attracted to the region of positive charge. The electrons migrate towards the left side of the sphere until there is a uniform distribution of positive charge. When an oil tanker car has arrived at its destination, it prepares to empty its fuel into a reservoir or tank.

Part of the preparation involves connecting the body of the tanker car with a metal wire to the ground.