How can objects become charged

The duster is rubbed back and forth along the rod. Electrons carrying a negative charge are transferred and now reside on the duster. When a polythene rod is rubbed with a duster, the friction causes electrons to gain energy. If the rod is swapped for a different material such as acetate , electrons are rubbed off the acetate and onto the duster.

Both of the rods and the duster are made of insulating materials. Insulators prevent the electrons from moving and the charge remains static. 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. While the can is far away from the balloon, the negative charge on the balloon has little or no effect on the can, and the electrons on the can are evenly dispersed. When the balloon is brought near the can, something interesting happens — the electrons move to the side of the can to get as far away from the negatively charged balloon as possible.

This leaves the side of the can nearest the balloon positively charged. The can as a whole is still neutral, but because the positively charged side of the can is close to the balloon, the negative charges on the balloon attract the positive side of the can and the force pulls the balloon and can together.

If the can is lying on its side, it will roll towards the balloon. Something quite different happens if the conducting can is allowed to touch the charged balloon. When the balloon and can touch, some of the electrons on the balloon will flow onto the can, leaving the can with extra electrons and therefore negatively charged.

Now both the balloon and can are negatively charged, and the like charges cause a force pushing the can and balloon apart. If the can is lying on its side, it will roll away the balloon. In the above example, we used a negatively charged balloon to impart a negative charge to the can by a process of direct contact. It is also possible to use a negatively charged balloon to impart a positive charge on a can through a process called induction.

If the balloon is brought near the can, the electrons move to the far side of the can, as described earlier. If another object, like a finger, now touches the negative side of the can, some of the overcrowded electrons will flow onto the object, leaving the can positively charged. In all the above examples, the charging by conduction process involved the touching of two conductors.

Does contact charging have to occur through the contact of two conductors? Can an insulator conduct a charge to another object upon touching? And can an insulator be charged by conduction? A complete discussion of these questions can get messy and quite often leads to a splitting of hairs over the definition of conduction and the distinction between conductors and insulators. The belief is taken here that only a conductor can conduct charge to another conductor.

The process of noticeably charging an object by contact involves the two contacting objects momentarily sharing the net excess charge. The excess charge is simply given a larger area over which to spread in order to reduce the total amount of repulsive forces between them.

This process demands that the objects be conductors in order for electrons to move about and redistribute themselves. An insulator hinders such a movement of electrons between touching objects and about the surfaces of the objects.

This is observed if an aluminum pie plate is placed upon a charged foam plate. When the neutral aluminum plate is placed upon the charged foam plate, the foam plate does not conduct its charge to the aluminum. Despite the fact that the two surfaces were in contact, charging by contact or conduction did not occur. Or at least whatever charge transfer might have occurred was not noticeable by the customary means of using an electroscope, using a charge testing bulb or testing for its repulsion with a like-charged object.

Many might quickly suggest that they have used a charged insulator to charge a neutral electroscope or some other object by contact.

In fact, a negatively charged plastic golf tube can used to charge an electroscope. The plastic tube is touched to the top plate of the electroscope. On most occasions, the plastic tube is even rubbed or rolled across the plate of the electroscope? Wouldn't this be regarded as charging by conduction? Not really. In this case, it is more than likely that the charging occurred by some process other than conduction.

There was not a sharing of charge between the plastic tube and the metal parts of the electroscope. Of course, once some excess charge is acquired by the electroscope, that excess charge distributes itself about the surface of the electroscope. Yet the charge is not uniformly shared between the two objects.

The protons and electrons within both the plastic golf tube and the electroscope are not acting together to share excess charge and reduce the total amount of repulsive forces. The charging of an electroscope by contact with a negatively charged golf tube or any charged insulating object would best be described as charging by lightning. Rather than being a process in which the two objects act together to share the excess charge, the process could best be described as the successful effort of electrons to burst through the space air between objects.

The presence of a negatively charged plastic tube is capable of ionizing the air surrounding the tube and allowing excess electrons on the plastic tube to be conducted through the air to the electroscope. This transfer of charge can happen with or without touching. In fact, on a dry winter day the process of charging the metal electroscope with the charged insulator often occurs while the insulator is some distance away.

The dry air is more easily ionized and a greater quantity of electrons is capable of bursting through the space between the two objects.

On such occasions, a crackling sound is often heard and a flash of light is seen if the room is darkened. This phenomenon, occurring from several centimeters away, certainly does not fit the description of contact charging. A charged insulating object is certainly capable of transferring its charge to another object. The result of the charge transfer will be the same as the result of charging by conduction.

Both objects will have the same type of charge and the flow of electrons is in the same direction. However, the process and the underlying explanations are considerably different.