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Electrostatics

Electrostatics. Chapter 32 Notes. Electrical Forces. Electrical forces are billions and billions of times stronger than gravitational forces. They pull on you all the time. How come you are not squished flat?

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Electrostatics

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  1. Electrostatics Chapter 32 Notes

  2. Electrical Forces • Electrical forces are billions and billions of times stronger than gravitational forces. • They pull on you all the time. • How come you are not squished flat? • In addition to the attractive force, there is a repulsive force that is also billions and billions of times stronger than gravity. These forces cancel- no net force! • Electrical forces arise from particles in atoms.

  3. Electrical Charge • The protons in the nucleus attract the electrons and keep them in orbit. • Electrons are attracted to protons, but repel other electrons. • This behavior is due to a property called charge. • Electrons –negatively charged • Protons – positively charged • Like charges repel; opposite charges attract!

  4. Conservation of Charge • Electrons and protons have electric charge. The charge is equal in magnitude, but opposite in sign. • Matter is made of atoms, atoms are made of electrons, protons, and neutrons. An object with equal numbers of protons and electrons has no net charge. • An object becomes electrically charged by adding or removing electrons. • Electrons are neither created nor destroyed, they are only transferred.

  5. Coulomb’s Law • Recall Newton’s Law of Gravitation. • The electrical force between any two objects obeys a similar inverse-square relationship. For charged particles, the force between the charges varies directly as the product of the charges and inversely as the square of the distance between them.

  6. Coulomb’s Law • The unit of charge is the coulomb, abbreviated C • The constant k (the Coulomb’s law constant) has a value of • In the equation, r is a unit of distance, and is measured in meters • You may use d instead

  7. Conductors and Insulators • Electrons move more easily in some materials than in others. • Conductors: outer electrons are not tightly bound, e.g. most metals • Insulators: outer electrons are tightly bound and remain with particular atoms, e.g. rubber, glass

  8. Charging by Friction and Contact • Charging by Friction: electrons are transferred when one material rubs against another • Example: • Charging by Contact: electrons are transferred from one material to another by simply touching • Example: when a charged rod is placed in contact with a neutral object, some charge will transfer to the neutral object

  9. Charging by Induction • Bringing a charged object near a conducting surface will make electrons move • Charge induction by grounding: • Grounding: allowing a conducting path to a practically infinite reservoir for electric charge

  10. Charge Polarization • Charging by induction in insulators • Rearrangement of the positions of charges within the atoms and molecules • When one side of an atom or molecule is slightly more negative or positive than the other it becomes electrically polarized

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