Electric Charges Electricity Unit

Exploring Static Charges Electricity is a form of energy that results from the interaction of charged particles, such as electrons or protons. Static charge (or static electricity) is an electric charge that tends to stay on the surface of an object, rather than flowing away quickly. Static = stationary or not moving

Static charges build up as different materials rub together, such as in a clothes dryer. This is called charging by friction = a process in which objects made from different materials rub against each other, producing a net static charge on each. When objects become charged by friction, one material has a stronger material, and therefore pulls electrons off the material that has the weaker attraction for electrons.

As a result, both materials become charged due to an excess or a deficit (shortage) of electrons. Remember back to the Bohr-Rutherford Model of the Atom, in which electrons move in the outer parts of the atom, relatively far from the nucleus. Electrons are negatively charged.

Charged objects exert an electric force on each other. Objects with like charges repel each other; objects with opposite charges attract each other. This is called the Law of Electric Charges.

The B-R model of the atom explains the following: Particles that carry electric charges can be neither created nor destroyed. Any net charge on a solid object, whether it is positive or negative, results from the transfer of electrons from one object to another. Compared with a neutral object, an object with an excess of electrons (more electrons than protons) has a negative charge.

Compared with a neutral object, an object with a deficit of electrons (fewer electrons than protons) has a positive charge. Remember, protons have a positive charge. Different materials hold on to their electrons with different strengths. See the Electrostatic Series.

An electrostatic series is a list of materials that have been arranged according to their ability to hold on to electrons. If we rub together two materials that are far apart in an electrostatic series, we can accurately predict the charge on each that will result.

Electrons can move each from one atom to another. When electrons move, they transfer electric charges. Protons do not move from one atom to another. Neutral objects have an equal number of protons and neutrons.

When a neutral object gains electrons, it becomes negatively charged. When a neutral object loses electrons, it becomes positively charged. Electric force increases with an increase in electric charge and decreases with increasing distance between the objects.

Moving Charges A conductor is a material that transmits thermal energy or electrical energy easily. Metals such as copper wire are considered good conductors. An insulator is a material, such as ceramic, which prevents the flow of electrons. Most non-metals are insulators.

Electrical conductivity is a material’s relative ability to conduct electricity and allow electrons to flow through it. Different materials fall along a range that based on increasing levels of conductivity.

Grounding: removing static charges The simplest way to remove the net static charge on an object is to put it in contact with a ground = an object that can supply a very large number of electrons to, or can remove a very large number of electrons from, a charged object, thus neutralizing the object. In many situations, static charges are a serious hazard to both people and electrical equipment.

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