ch17_dgrk

Chapter 17 Electric Forces and Fields __Section 17.1 electric charge__ __** Section 17.2 Electric Force **__
 * Charges are always positive or negative, never both.
 * Like charges repel(positive and positive or negative and negative)
 * Unlike charges attract(positive and negative)
 * Positively charged particles are called **protons**
 * Negatively charged particles are called **electrons**. They are located outside the nucleus and move freely around it.
 * **Electrons** can also move from atom to atom
 * Neutrally charged particles are called **neutrons**
 * Protons and neutrons are relatively in fixed positions in the nucleus.
 * **Energy is always conserved and cannot be created or destroyed**
 * A **conductor** is a material in which electric charges can flow freely. Examples:copper and aluminum as well as most metals
 * An **insulator** is a material in which electric charges cannot flow freely. Examples: glass, rubber,silk, and plastic.
 * There is a third group called **semiconductors** in their pure state semiconductors are insulators but they can be altered to be conductors. Examples:silicon and germanium
 * Insulators and conductors can be charged by contact
 * A conductor can go through **induction** they can be charged by bringing another charged object near it and allowing the displaced charge to drain off the side. Then removing the drain while the charged obeject is still there. Lastly the original charged object is removed and the charge is induced.
 * **Polarization** is another way to change charge. In the presence of a charged object the centers of positive and negative changes shift slightly giving the atom a temporary charge.
 * Kc is known as **coulombs constant** and it is equal to 8.9875 x 10^9 Nm^2/C^2
 * The closer two charges are the greater the force between them is
 * There are electric and gravitational forces
 * **Electric forces** can be attractive or repulsive **Gravitational forces** are always attractive
 * Electric forces are much more powerful than gravitational forces

**__Section 17.3 The Electric Field__**


 * In the space around it a charged object has an electric field
 * When another charged atom these objects electric fields are forced to interact
 * The SI unit for electric field is Newton per Coulmb
 * The electric field is a vector quantity
 * The direction of E depends on the sign of the charge produced by the field because it will either attract or repel from the field depending on the charge
 * According to Coulmbs law a test charge will cause a rearrangement of the of the charges in an atomical sphere.
 * **Electric Field Lines** do not really exist, but they are useful in analyzing fields by representing both the strength and the direction of the field at different points in space.
 * Electric field lines are drawn so that the electric field vector is tangent to the lines at each point.
 * Electric field is stronger the closer the field lines are to each other and as the lines are furthur apart it is weaker.
 * There are rules for drawing electric field lines. The lines must begin on positive charges or at infinity and must terminate on negative charges or infinity.
 * The number of lines drawn leaving a positive charge or approaching a negative charge is proportional to the magnitude of the charge.
 * No two field lines from the same field can cross each other.
 * A good conductor such as copper contains charges that are not bound to any atoms and are free to move within the material
 * When no net motion is occurring the conductor is said to be in electrostatic equilibrium
 * All conductors said to be in electrostatic equilibrium have an electric field of zero everywhere inside the conductor
 * Any excess charge on an isolated conductor is entirelyy on the surface of the conductor
 * The electric field immediatley outside of a charved conductor is perpendicular to the surface of the conductor
 * On an irregularly shaped conductor the charge will tend to accumulate where the radius of outward curvature is smallest

__ Electric Field Line Drawings __

These picture were provided by the Holt, Rinehart and Winston Physics book

Equations Coulomb's Law math F_{electric}=k_C(\frac{q_1q_2}{r^2}) math

math E=\frac{F_{electric}}{q0} math

math E=\frac{k_Cq}{r^2} math

math F_g=G(\frac{m_em_p}{r^2}}) math

Example Problems

This problem was provided from the Holt Physics book This problem was provided by the Holt Physics Book

Source Serway, and Faughn. __Holt Physics__. New York: Holt Rinehart & Winston, 2002.