Electron Movement in Objects

Electron Movement in Objects

CONDUCTORS VS. INSULATORS

What is true of atoms in terms of being neutral, negatively charged, and positively charged is also

true of objects. Objects can work like ions by losing or gaining electrons.

CONDUCTORS VS INSULATORS

The behavior of an object which has been charged is dependent upon whether the object is made of a conductive or a nonconductive material.

A material with easily detached electrons (which can then move through the material somewhat freely) is referred to as a conductor. Conductors are materials which permit electrons to flow freely from atom to atom and molecule to molecule. Metals are good conductors because some electrons in the atoms are free to move throughout the metal. The Earth is also a good conductor.

In contrast to conductors, insulators are materials which resist the free flow of electrons from atom to atom and molecule to molecule because their electrons are strongly attached. If charge is transferred to an insulator at a given location, the excess charge will remain at the initial location of charging. So insulators are good at generating and holding a surface charge because the particles of the insulator do not permit the free flow of electrons.

What does this chart mean?

Methods of Charging Objects

THE LAW OF CONSERVATION OF CHARGE

THE LAW OF CONSERVATION OF CHARGE

Charge is neither created nor destroyed. When objects are charged, electrons are transferred from one object to another or they move within the object. No matter what type of charging method is used, the amount of charge present in the system before charging will be the same as the amount of charge present in the system after the charging. This is referred to as the law of conservation of charge.

Well, how do objects get charged to begin with? There are three methods of charging: friction, induction and conduction.

FRICTION

Friction results in a transfer of electrons between two electrically neutral objects which are rubbed together. The two objects become oppositely charged as a result of the transfer of electrons.

Different materials are made of different atoms – with different electron affinities. Simply put, the property of electron affinity refers to the relative amount of love which a material has for electrons. If atoms of a material have a high electron affinity, then that material will have a relatively high love for electrons.

A triboelectric seriesis a listing of materials in order of their relative attraction for the electrons of another material. Materials listed near the top of the table have a stronger affinity for electrons than those located below them. When any two materials in the table are rubbed together, the one which is higher can be expected to pull electrons from the material which is lower. As such, the materials highest on the table will have the greatest tendency to acquire the negative charge. Those below it would become positively charged.

CONDUCTION

Charging by conduction involves the contact of a charged object to a neutral object. When a charged object touches a neutral object, electrons flow from one object to the other attempting to equalize the charge on both objects. The objects need to be conductors. Conduction doesn’t work as well with insulators because they do not allow charge to spread out.

INDUCTION

Charge induction occurs when a charged object causes electrons on the surface of a second neutral object to either move toward or away from the charged object without the two objects actually touching. This is called separation of charge and serves to create areas in the second object that are unevenly charged. The unevenly charged object is said to be polarized. Because the charged object doesn’t touch the neutral object, there is no transfer of charge (electrons).

Effects on conducting materials…

When the originally neutral object is a conductor, its electrons are loosely bound so they can move from one part of the object to another part. If a negatively charged object is brought near a neutral conducting object (1), it will cause electrons to move away from the negatively charged object and the positive charges to move toward the negatively charged object (2). Overall the object is electrically neutral; it's just that the positive and negative charge has been separated from each other. We say that the charge in the object has been polarized within the object.

If the originally neutral object is a grounded conductor (3), the negative charge will flow to the earth and the entire object will become positive (4). If is NOT grounded, it will return to its neutral state once the charged object moves away.

Effects on insulating materials…

Electrons aren’t free to move in an insulator – but that does not mean that an insulator doesn’t experience polarization. Polarization in an insulator is a result of an alignment of the charge within each individual molecule. So when induction happens to an insulator, the particles in the insulator realign themselves creating a polarized object. Charge builds up and stays there (creating static electricity).