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Electrostatics

Electrostatics. Electrostatics: the study of electricity at rest involves electric charges, the forces between them, and their behavior in materials Ex: getting shocked by door handle, hair sticking up when putting on a sweater in the winter. Four Important Facts About Atoms.

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Electrostatics

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  1. Electrostatics Electrostatics: the study of electricity at rest involves electric charges, the forces between them, and their behavior in materials Ex: getting shocked by door handle, hair sticking up when putting on a sweater in the winter

  2. Four Important Facts About Atoms • Every atom has a (+) charged nucleus surrounded by (-) charged electrons. • All electrons are identical • The nucleus is composed of protons and neutrons. All protons are identical. All neutrons are identical. • Atoms usually have equal numbers of protons and electrons so their net charge is zero.

  3. Electrical Forces and Charges • An electrical force is a force that one charge exerts on another. • Electrical forces are stronger than gravitational forces. • Electrical forces arise from the particles inside an atom

  4. Charge: the fundamental electrical property to which mutual attractions or repulsions b/w electrons or protons is attributed. • Like charges repel; opposites charges attract • SI Unit: coulomb (C) • There are 6.24 X 1018 electrons in one coulomb • Ex: 2 electrons push away from each other, an electron and a proton are attracted and pull towards each other

  5. Conservation of Charge • Atoms remain neutral by maintaining equal numbers of (+) and (-) charges. • A charged atom is called an ion. • An imbalance of charge is produced by adding or removing electrons.

  6. The Law of Conservation of Charge: Charge cannot be created or destroyed • Charges can only move from one atom/object to another • Ex: If you rub a rubber rod with a piece of fur, electrons are transferred from the fur to the rod. The fur becomes (+) charged, the rod becomes (-) charged.

  7. Check Your Understanding If you scuff electrons onto your feet while walking across a rug, are you negatively or positively charged? • Negatively charged. You are adding electrons to yourself. Is the rug negatively or positively charged? • Positively charged. You are taking electrons away from the rug, making the rug less negative…and therefore more positive.

  8. Coulomb’s Law Coulomb’s Law: the relationship among electrical force, charges, and distance. The electrical force b/w 2 charges varies directly as the product of the charges and inversely as the square of the distance b/w them. • The bigger the charges, the bigger the electrical force • The further apart the charges, the less the electrical force • SI Unit: Newtons (N)

  9. Equation: F = k(q1q2) d2 • F = electrical force (Newtons) • k = electrical force constant • q1 = charge 1 (coulomb) • q2 = charge 2 (coulomb) • d = distance b/w charges (meters)

  10. Check Your Understanding If you double one charge, what happens to the electrical force? • It doubles If you double both charges, what happens to the electrical force? • It quadruples If you double the distance between the charges, but the charges remain the same, what happens to the electrical force? • It is cut to 1/4th.

  11. Conductors and Insulators • Whether a substance is classified as a conductor or an insulator depends on how strongly the atoms of the substance hold their electrons. • A conductor is a material through which electrical charge can flow. • Metals are good conductors b/c the electrons are loosely bound. • An insulator is a material through which electrical charge cannot flow. • Plastics are good insulators b/c the electrons are tightly bound.

  12. A semiconductor behaves as both an insulator and a conductor. • Transistors are examples of semiconductors. • Certain metal, at absolute zero, acquire infinite conductivity. These metals are called superconductors. • Once electric current is established in superconductor, the electrons flow indefinitely.

  13. Check Your Understanding Is aluminum a good conductor or insulator of electricity? • A good conductor. Good heat conductors are generally good electrical conductors. Are the electrons tightly or loosely bound then? • Loosely bound. The electrons’ ability to “bump” into each other allows electricity to travel.

  14. Check Your Understanding Is water a good conductor or insulator of electricity? • A good conductor of electricity. That’s why it is so dangerous to have electrical devices near water; the water can carry the electricity from the device to you, thereby electrocuting you.

  15. Check Your Understanding Why are some electrical wires made to have copper wires wrapped in rubber? • B/c copper is a good conductor, moving electricity from the outlet to the device. It is wrapped in rubber b/c rubber is a good insulator, preventing the electricity from leaving the wire and entering your body.

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