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Electrostatics

Electrostatics. Physics. Electrostatics. Electricity is responsible for lightening, static from carpet & a force holding atoms together. Electrostatics is the study of electricity at rest . Electrostatics involves electric charges, the forces between them and their behavior in materials.

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Electrostatics

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  1. Electrostatics Physics

  2. Electrostatics • Electricity is responsible for lightening, static from carpet & a force holding atoms together. • Electrostatics is the study of electricity at rest. • Electrostatics involves electric charges, the forces between them and their behavior in materials.

  3. Electric Terms • The aura that surrounds electric charges is called the electric field. • Electric currents are moving electric charges.

  4. Electrical Forces • Electrical forces arise from sub-atomic particles. • Atom consists of a nucleus (+) surrounded by electrons (-). • p+ attract e- & hold them in place • E- are repelled by other e- that are orbiting the nucleus. • Neutrons, in nucleus. have no charge. • Rule of electrical phenomenon is, “like charges repel; opposite charges attract.”

  5. Conservation of Charge • In a neutral atom, there are an equal number of e- & p+, so there is no net charge. • If an e- is removed, the atom becomes positively charged. • If a p+ is removed, the atom becomes negatively charged. • A charged atom is called an ion.

  6. Matter • Matter is made of atoms which are made of e-& p+. • If an imbalance of charges occurs by adding or removing e- then the object becomes electrically charged. • The outermost electrons of many atoms are only loosely bonded. • The amount of energy needed to remove an e- depends upon thesubstance.

  7. Transfer of Electrons • Charge is always conserved. • Chargers are neither created nor destroyed, simply transferred from one object to another. • Any object that is electrically charged has an excess or deficiency of a whole number of e-, never fractions of e-.

  8. Electrical Force & Distance • The electrical force between any two objects has a similar relationship with distance as Newton’s law of gravity. F = G(m1m2/d2) • It was calculated by French physicist Charles Coulomb in the 18th century.

  9. Coulomb’s Law • “that for charged particles/objects, the force between the charges varies directly as the product of the charges & inversely as the square of the distance between.” or, F = k(q1q2/d2) where, • d = distance • q1 is the quantity of charge of one particle • q2 is the quantity of charge of the 2nd particle • k is the proportionality constant.

  10. The Coulomb • The SI unit of charge is the coulomb or C. • 1 coulomb (C) is the charge of 6.24 x 1018 electrons. • Which is about the amount of charge that passes through a 100 watt bulb in 1 second.

  11. Proportionality Constant (k) • The proportionality constant (k) is similar to the constant of gravity. • It is a very large number, • k = 9, 000 000 000 Nm2/C2 or, 9.0 x 109

  12. Comparing Electrical Forces & Gravity • The equations for the force of gravity and the force of electrical forces are very similar. • However, while gravity is very small between small masses, strength of electrical attraction can be very strong between small masses. • . • Also gravity can only attract, while electrical forces can attract AND repel.

  13. Strength of Electrical Forces • In most objects, e- & p+ are equal & therefore electrical forces are balanced & not noticeable. • However, at the atomic level electrical forces working at the atomic level are responsible for bonding & molecules.

  14. Conductors & Insulators • Electrons are more easily moved in certain materials called conductors. • Metals are good conductors because their e- are “loose.” (sea of electrons) • Electrons are tightly bound in other materials & not free to move around (insulators)

  15. Semiconductors & Superconductors • sometimes act as insulators & sometimes act as conductors are called semiconductors. • Used in transistors, microchips. • Superconductors are metals that acquire infinite conductivity near absolute zero. Used in mag-lev trains

  16. Charging by Friction & Contact • When a charged rod is placed in contact with a neutral object, some of the charge is transferred. • Electrons can be transferred by friction when one material rubs against another.

  17. Charging by Induction • Charging by induction occurs when a charged object is brought near to a conducting surface. • The e- on the charged object will move to the conducting surface. • This is called inducing a charge.

  18. Grounding • Grounding occurs when charges that repel each other have a conducting path to a near infinite reservoir of charges, the ground.

  19. Charge Polarization • Charging by induction is not restricted to conductors. • When a charge rod is brought near an insulator, the position of charges within the atoms themselves is rearranged. • The atoms or molecule becomes slightly more positive on one side and negative on the other. • The atom or molecule electrically polarized.

  20. Charge Polarization Electric Dipoles Many molecules—H2O, for example—are electrically polarized in their normal states. There is a little more negative charge on one side of the molecule than on the other. Such molecules are said to be electric dipoles, or polar molecules.

  21. Charge Polarization Charged combs attract uncharged paper because the force of attraction for the closer charge is greater than the force of repulsion for the farther charge..

  22. Charge Polarization -An inflated balloon rubbed on your hair becomes charged. Place balloon against wall and it sticks. -The charge on balloon induces an opposite surface charge on wall. I’s tslightly closer to the opposite induced charge than to the charge of the same sign.

  23. Assessment Questions • If a neutral atom has 22 protons in its nucleus, the number of surrounding electrons is • less than 22. • 22. • more than 22. • unknown.

  24. Assessment Questions • If a neutral atom has 22 protons in its nucleus, the number of surrounding electrons is • less than 22. • 22. • more than 22. • unknown. Answer: B

  25. Assessment Questions • When we say charge is conserved, we mean that charge can • be saved, like money in a bank. • only be transferred from one place to another. • take equivalent forms. • be created or destroyed, as in nuclear reactions.

  26. Assessment Questions • When we say charge is conserved, we mean that charge can • be saved, like money in a bank. • only be transferred from one place to another. • take equivalent forms. • be created or destroyed, as in nuclear reactions. Answer: B

  27. Assessment Questions • A difference between Newton’s law of gravity and Coulomb’s law is that only one of these • is a fundamental physical law. • uses a proportionality constant. • invokes the inverse-square law. • involves repulsive as well as attractive forces.

  28. Assessment Questions • A difference between Newton’s law of gravity and Coulomb’s law is that only one of these • is a fundamental physical law. • uses a proportionality constant. • invokes the inverse-square law. • involves repulsive as well as attractive forces. Answer: D

  29. Assessment Questions • Which is the predominant carrier of charge in copper wire? • electrons • protons • ions • neutrons

  30. Assessment Questions • Which is the predominant carrier of charge in copper wire? • electrons • protons • ions • neutrons Answer: A

  31. Assessment Questions • When you scuff electrons off a rug with your shoes, your shoes are then • negatively charged. • positively charged. • ionic. • electrically neutral.

  32. Assessment Questions • When you scuff electrons off a rug with your shoes, your shoes are then • negatively charged. • positively charged. • ionic. • electrically neutral. Answer: A

  33. Assessment Questions • When a cloud that is negatively charged on its bottom and positively charged on its top moves over the ground below, the ground acquires • a negative charge. • a positive charge. • no charge since the cloud is electrically neutral. • an electrically grounded state.

  34. Assessment Questions • When a cloud that is negatively charged on its bottom and positively charged on its top moves over the ground below, the ground acquires • a negative charge. • a positive charge. • no charge since the cloud is electrically neutral. • an electrically grounded state. Answer: B

  35. Assessment Questions • When a negatively charged balloon is placed against a non-conducting wall, positive charges in the wall are • too bound to negative charges in the wall to have any effect. • repelled from the balloon. • attracted to the balloon. • neutralized.

  36. Assessment Questions • When a negatively charged balloon is placed against a non-conducting wall, positive charges in the wall are • too bound to negative charges in the wall to have any effect. • repelled from the balloon. • attracted to the balloon. • neutralized. Answer: C

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