ch32_cdhw

**Chapter 32: Electrostatics** Definitions: 32.1: **Electrical forces**: A force that one charge exerts on another. When the charges are the same signe, they repel; when the charges are opposite, they attract. 32.1:**Charge**: The fundamental electrical property to which the mutual attractions or repulsions between electrons or protons is attributed. 32.2: **Conservation of Charge**: The principle that net electric charge is neither created nor destroyed but is transferable from one material to another. 32.3: **Coulomb's Law**: The relationship among electrical force, charges, and distance: The electrical force between two charges varies directly as the product of the charges and incersely as the square of the distance between them. 32.3: **Coulomb**: Si unit of charge. One coulomb is equal to the toal charge of 6.24 X 10^18 electrons. 32.4: **Conductors**: Material, usually a metal, throgh which electric charge can flow. Good conductors of hear are generally good charge conductors. 32.4: **Insulators**: A material that is a poor conductor of electricity. 32.4: **Semi-conductors**: Materials that can be made to behave as either a conductor or an insulator 32.4: **Super conductors**: Material that has infinite conductiivity at ver low temperatures so that charge flows through it without resistance. 32.6: **Induced**: Term applied to electric charge that has been redistributed on an object because of the presence of a charged object nearby. 32.6: **Induction**: The charging of an object without direct contact. 32.6: **Grounding**: Allowing charges to move freely along a connection between a conductor and the cround. 32.7: **Electrically polarized**: Term applied to an ator or molecule in which the charges are aligned so that one side is slightly more positive or negative than the opposite side.

All definitions draw from //Conceptual Physics: Third Edition.//

**//32.1: Electrical Forces and Charges//** Electrical forces are two forces acting on you that balance one another out, and have no noticable affect. These forces come from particles and atoms in the Earth's atmosphere. Electrons are attracted to protons, but they repel other protons. This is due to a property called **charge**. Electrons are negatively charged, protons are positively charged, and neutrons are neutraly charged. There is a positively charged nucleus at the center of every atom, surrounded by negative electrons. Every electron has the same mass and negative charge. Atoms have a 0 net charge, meaning the postive and negative charges balance one another out. Like charges, like two positive or two negative atoms, repel one another, while opposite charges, like one positive and one negative, attract one another.

//**32.2: Conservation of Charge**// In a neutral atom, there are as many electrons as protons, creating a 0 net charge on the atom. If an electron is taken from an atom, the atom isn't neutral anymore, and is positively charged with a +1 charge. A charged atom is also called an ion. When an ion is positive, one or more electrons has been taken away. When an ion is negative, it has gained additional electrons. In an atom, the electrons closest to the nucleus are very tightly compacted, but the one farther away can be removed easily. The energy needed to remove an electron varies between elements. In rubber, electrons are more tightly bound than in human hair. Electrons can't be created or destoryed, only moved. That's because charge is always conserved. Electrons can't be divided into fractions, and must remain as a whole.

//**32.3: Coulomb's Law**// The electrical force between objects is similar to the inverse square relationship with distance and gravity. Coulomb's Law states "For charged particles or objects that are small compared with the distance between them, the force between the charges varies directly as a product of the charges and inversely as the square of the distance between them." The law can be expressed as //F= k((q1q2)/d^2).// In this formula, //d// is the distance between the charged particles or ions, //q1// is the quantity of charge of one particle, and //q2// is the quantity of the other charge. //K// is the proportionality constant, which is equal to 9.0 X 10^9 (Nm^2)/C^2. The coulomb is the SI unit used to measure charge. It is abbreviated as C. The charge of 1 C is the charge of 6.24 billion billion electrons. This is also the amount of charge the goes through a 100 W light blub in one second. The electrical force between two 1 C charges is extremely powerful. Since most objects are neutral, the forces balance one another out and there is no electrical force between the two.

//**32.4: Conductors and Insulators**// Electrons are more easily moved in some materials. These materials are called **conductors**. Electrons in other materials are tightly bound, and these objects are called **insulators**. All materials can be arranged in order of their ability to conduct electric charges. The conductors are at the top of the list and the insulators are at the bottom. Materials that behave as insulators and conductors both are called **semiconductors**. Layering semicondutor materials is the way to create transistors. At temperatures near absolute zero, some metals become infinitely conductive. These are called **superconductors**.

//**32.5: Charging by Friction and Contact**// By simply touching, electrons can be transfered between materials. Placing a charged rod in contact with a neutral object causes some of the charge to be transfered into the neutral object it's touching. This is called charging by contact. If the neutral object is a good conductor, the charge will spread out to all parts of the surface of the object because the like charges repel one another. If it is a bad conductor, the charge rod would have to touch many places on the neutral object to get an even spread of charge on the object's surface.

If a charged object is brought near a conducting object even without touching electrons will move into the conducting object. Through this process a charge has been **induced** in the object. When the charged object is removed the objects are charged equally and oppositely, and the object have been charged by **induction**. If a metal sphere is hanging from a string, it has a net charge of zero. If a charged rod is brought near the sphere, a charged redistribution occurs in the sphere, however it's net charge is still zero. When you touch the sphere it removes the electrons and the sphere is left with a positive charge. A negative rod is then touched to the sphere and electrons move from the sphere to the rod and the two repel each other. The sphere has been negatively charged through contact. When a metal surface is touched with a finger the charges repel and continue through your body to the ground. This is called **grounding**.
 * //32.6: Charging by Induction//**

//**32.7: Charge Polarization**// Chargin by induction does not only apply to conductors. When a charged object is brough near an insulator, the electrons in the insulator are not free to move around. Instead the arrangement of charges in atoms of the insolator change. One side of the atom becomes more positive or negative than the other side, and the atom has become **electrically polarized**. If the charged object brought near the insulator was positive the negative side of the atom would be closer to the charged object. This occurs when you rub a ballon on your hair and stick it to a wall. The ballon has gained a negative charge by taking electrons from your hair. When the ballon is placed against the wall the negative charge of the ballon induces opposite surface charge on the wall, causing the part of the wall closest to the ballon to be positively charged.