Créer une présentation
Télécharger la présentation

Télécharger la présentation
## Welcome to Physics 112

- - - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - - -

**Welcome to Physics 112**• Instructor: Mike Talbot • Web Page : delta.edu/mttalbot/physics112**Chapter 15**Electric Forces and Electric Fields**Introduction**• Greek contributions (700 BC) • Friction generates electricity • Rub a piece of amber with wool 61**Introduction**• Charged particles • What are they? • What colors are they?**Introduction**• Coulomb’s Law • What does it say?**Introduction**• Electric fields • What is a gravitational field? • What is an electric field?**Properties of Electric Charges**• An electroscope may be used to demonstrate the existence of electrostatic forces. • It detects and identifies charges produced by such things as: • Plastic combs • Glass and silk • Hard rubber and wool • Balloons 62, 15.1**Properties of Electric Charges**• Walking across a carpet in the winter can also generate static electricity.**Properties of Electric Charges**• Dust accumulates on a TV screen because of the large static charge on the glass.**Properties of Electric Charges**• What should you do if a power line falls on your car while you are in it?**Properties of Electric Charges**• How many kinds of charge exist?**Properties of Electric Charges**• How many kinds of charge exist? • Two**Properties of Electric Charges**• Two kinds of charge (+ and -) • Named by Benjamin Franklin**Properties of Electric Charges**• Law of Charges 155**Properties of Electric Charges**• Law of Charges • At least two particles are involved • Like charges repel, opposites attract. • Motion may result**Properties of Electric Charges**• Law of Charges • At least two particles are involved • Like charges repel, opposites attract. • Motion may result • Planetary model of the atom 125**Properties of Electric Charges**• Are atoms neutral?**Properties of Electric Charges**• What is meant by the conservation of charge?**Properties of Electric Charges**• What is meant by the quantization of charge (e)**Properties of Electric Charges**• Demonstrating the quantization of charge (e) • The Millikan Oil-Drop Experiment • Measured the elementary charge on an electron 15.21**Insulators and Conductors**• Materials may be classified by their ability to conduct electricity.**Insulators and Conductors**• Materials may be classified by their ability to conduct electricity. • Conductors (many free electrons) • Insulators (few free electrons)**Insulators and Conductors**• Materials may be classified by their ability to conduct electricity. • Conductors (many free electrons) • Insulators (few free electrons) • Semiconductors**Insulators and Conductors**• What are some examples of good conductors?**Insulators and Conductors**• What are some examples of good insulators?**Insulators and Conductors**• What is an example of asemiconductor? • Where are semiconductors used? 225**Grounding**127**Insulators and Conductors**• Polarization of charge**Coulomb’s Law**• An electric force has three properties: 15.6**Coulomb’s Law**• An electric force has three properties: • It is attractive or repulsive depending upon the sign of the charges.**Coulomb’s Law**• An electric force has three properties: • It is attractive or repulsive depending upon the sign of the charges. • It is directly proportional to the product of the magnitudes of the charges (q1.q2).**Coulomb’s Law**• An electric force has three properties: • It is attractive or repulsive depending upon the sign of the charges. • It is directly proportional to the product of the magnitudes of the charges (q1.q2). • It is inversely proportional to the square of the separation (r2).**Coulomb’s Law**• Coulomb’s formula:**Coulomb’s Law**• Definitions • Coulomb • The amount of charge that has passed a given point in one second when one ampere of current is flowing**Coulomb’s Law**• Definitions • Ampere • One coulomb of charge passing a given point in one second • Analogy: Like water flowing through a pipe**Coulomb’s Law**• Coulomb’s constant: ke = 8.9875 x 10 9 N.m2/C2**Coulomb’s Law**• Charges and masses of particles • Table 15.1 (pg. 501)**Coulomb’s Law**• Reminders: • Force is a vector quantity • r is the distance between centers • Newton’s Third Law applies • The Coulomb force is a field force just like …?**Coulomb’s Law**• Reminders: • Force is a vector quantity. • r is the distance between centers. • Newton’s Third Law applies. • The Coulomb force is a field force just likegravity.**Coulomb’s Law**• The two field force formulas are mathematically identical.**Coulomb’s Law**• The two field force formulas are mathematically identical. F = k q1q2/r2**Coulomb’s Law**• The two field force formulas are mathematically identical. F = k q1q2/r2 F = G m1m2/r2**Coulomb’s Law**• Differences between electrical and gravitational forces • Gravity only attracts