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Chapter 5: Electricity and Magnetism

Chapter 5: Electricity and Magnetism. Electricity and Magnetism. What is Electricity?. Electricity describes all the phenomena caused by positive and negative charges. Negatively charged bodies contain more electrons than protons. Positive charged bodies contain more protons than electrons.

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Chapter 5: Electricity and Magnetism

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  1. Chapter 5: Electricity and Magnetism

  2. Electricity and Magnetism

  3. What is Electricity? Electricity describes all the phenomena caused by positive and negative charges. Negatively charged bodies contain more electrons than protons. Positive charged bodies contain more protons than electrons.

  4. What is Electricity? The charge of one electron or proton has a value of: 1.602x10-19 C (C: Coulomb)

  5. What is Electricity? 1 C = 6.25x1018 electrons or protons

  6. What is Electricity? + + Equal charges: repel each other Opposite charges: attract each other - +

  7. Conductors and Insulators Since most objects are electrically neutral, charging an object consists in creating an imbalance in the electrical charge of that object. Materials can be divided in three groups, according to their reaction to the process of “charging”: • Conductors • Semiconductors • Insulators

  8. Conductors and Insulators Conductors : permit the free flow of electrical charges. • Usually metals (weak attraction of valence electrons on the part of the atomic nucleus). • When charged, its electrons move in one general direction, pushing one another and making the charge move along the circuit. • Electrolytic solutions are also conductors (ions).

  9. Conductors and Insulators Insulators: impede the free flow of electrical charges. • Usually non-metals (strong attraction of valence electrons on the part of the atomic nucleus). • When charged, its electrons are strongly held by the atomic nuclei, so charges do not move. • Wood, glass, plastic, ceramics, paper, rubber, silk and air are also insulators.

  10. Static Electricity Describes all the phenomena related to electrical charges at rest. Metal-leaf electroscope: apparatus used to detect static electricity in an object (see Fig 5.11 on page 145 Textbook)

  11. Static Electricity Charging by friction: • Two neutral bodies rubbed against each other. • Some electrons are pulled from one of them. • Resulting: two opposite charged bodies (attraction!)

  12. Static Electricity Charging by conduction: • Two solid bodies in contact with each other. • The charge is transferred from the charged object to the second object. • Resulting: two equally charged bodies, each with less charge than initially

  13. Static Electricity Charging by induction: • One charged body (A) approaches a neutral one (B). • If B is a conductor: accumulation of equal amount of charges of opposite sign to those of A in the region of B closest to A. B remains after A is withdrawn. • If B is an insulator: accumulation of equal amount of charges of opposite sign to those of A in the region of B closest to A. B will discharge as soon as A is withdrawn.

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