Electrostatics (Electricity at rest)

Historical Approach How can an object be charged and what affect does that charge have upon other objects in its vicinity? The answer to this question begins with an understanding of the structure of matter.

Important facts about the atom: Every atom is composed of a positively charged nucleus surrounded by negatively charged electrons. The electrons of all atoms are identical. Each has the same quantity of negative charge and the same mass. Protons and neutrons compose the nucleus. Protons are about 1800 times more massive than electrons, but they carry an equal and opposite charge compared to the electron. Neutrons have slightly more mass than protons, but have no net charge. Atoms usually have as many electrons as protons, so the atom has zero net charge. In fact, all of the chemical bonding forces that hold atoms together to form molecules are electrical in nature.

How do you find the charge of an object (not just an atom)? Electric charge: Electric charge of an object can be positive, negative, or neutral. Neutral – same # of protons and electrons Negative – more electrons than protons Positive – more protons than electrons A charged atom is called an ION. It can have a positive charge or a negative charge. __________________________________________________________________ Like mass, the charge of an object is a measurable quantity: Charge is measured in units of Coulombs (abbreviated C). The charge on a single electron is -1.6 x 10^ -19 Coulomb. The charge on a single proton is +1.6 x 10^ -19 Coulomb. How do you find the charge of an object (not just an atom)?

How exactly does a charged object affect an uncharged object??? Electric force: How do charges affect each other? Opposite charges … ATTRACT! Like charges … REPEL! The electric force is a non-contact force (like gravity). This electric force exerted between two oppositely charged objects or two like charged objects is a force in the same sense that friction, tension, gravity, normal, and applied are forces. Any charged object can exert this force upon other objects - both charged or uncharged objects. How exactly does a charged object affect an uncharged object???

Big Idea!!! Is it easier to add or subtract electrons from an atom… or is it easier to add or subtract protons from an atom? The protons and neutrons are bound tightly together within the nucleus of the atom. Outside the nucleus are concentric spherical regions of space known as electron shells. The shells are the home of the negatively charged electrons. Each shell is characterized by a distinct energy level. Outer shells have higher energy levels and are characterized as being lower in stability. Electrons in higher energy shells can move down to lower energy shells; this movement is accompanied by the release of energy. Similarly, electrons in lower energy shells can be induced to move to the higher energy outer shells by the addition of energy to the atom. If provided sufficient energy, an electron can be removed from an atom and be freed from its attraction to the nucleus. Electrons are migratory and go where they are most wanted!

Electrostatics and materials: Conductor - materials that permit electrons to flow freely from atom to atom and molecule to molecule. Examples: metals, graphite, water, the human body, etc. Any excess charge will be distributed across the entire surface of the object. Insulator – materials that impede the free flow of electrons from atom to atom and molecule to molecule. Examples: plastic, Styrofoam, paper, rubber, glass, dry air, etc. Any excess charge will not be distributed across the surface, but will remain at the initial location of charging. Superconductor – materials that conduct electric charge through them without any loss of energy from heat. Perfectly conductive! Semiconductor – materials that are not good conductors, but can be made to act like a conductor some of the time (like silicon in transistors).