Chapter 21a - Electricity and Magnetism pervades our modern...

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Electricity and Magnetism pervades our modern world. We generate electric power (energy/second: Watts ) in power stations and transmit it down power lines to our homes where we use it for heating & cooling, lighting, cooking hot showers, computing, television, … and much more. While Its hard to imagine living without these wonderful modern conveniences electricity and magnetism are much more fundamental to our lives than even this suggests.
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Our understanding of the matter making up the world (including ourselves and all life) is that it is comprised of atoms of the elements: These atoms themselves are comprised of three, still smaller, constituents: Electrons , Protons and Neutrons
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The atom electron (~ 1/1000 mass of nucleons) proton neutron nucleons (comprise nucleus) Planetary model (Neils Bohr): electrons orbit around nucleus held in place by the electrostatic force . 4 He nucleon number – 2 protons + 2 neutrons in nucleus (2 electrons “orbiting”) ( 3 He also exists 2 p + , but 1 n (still 2 e - ) called an isotope) (This picture has been greatly refined by quantum mechanics but that’s another course you may get later. This model remains conceptually useful for our purposes.)
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The charge of the electron is 1.602 x 10 -19 C Electrons and protons have a property we call charge that is measured in units of Coulombs (C). 4 He The charge of the proton is + 1.602 x 10 -19 C Electrons and protons have charge of exactly the same magnitude but different sign . The significance of the sign is the following: Like charges (same sign) repel each other with the electrostatic force Opposite charges (opposite sign) attract with the electrostatic force Neutrons are neutral and are not affected by electrostatic forces. This smallest magnitude of charge is often designated e = 1.602 x 10 -19 C
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4 He Electrons and protons can be liberated from the atom to exist as free charged particles . Stable atoms are electrically neutral because they have an equal number of electrons and protons. Aluminum (Al) has 13 protons in its nucleus. To be electrically neutral it must have 13 electrons. If an atom of Al were missing 2 electrons it would have a charge of +2e. Placed in the vicinity of free electrons it would attract them with the electrostatic force, capturing 2 of them, after which it would become electrically neutral and no longer attract further electrons.
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Chapter 21a - Electricity and Magnetism pervades our modern...

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