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PHY 124: Introduction to Physics II Electricity and Magnetism Electric Forces and Fields. Kartik Ghosh. Why Electricity, Magnetism, Optics, and Modern Physics?. Understand the Nature. The Universe. Made of all particles that exist and the space where all events occur. Matters.
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PHY 124: Introduction to Physics IIElectricity and MagnetismElectric Forces and Fields Kartik Ghosh
Why Electricity, Magnetism, Optics, and Modern Physics? Understand the Nature
The Universe Made of all particles that exist and the space where all events occur
Matters Everything exists in the universe is made from tiny Atoms
Everything exists in the universe is made from tiny Atoms Fish Protein Amino Acid Atom: A very basic unit of matter
The Bohr Model of an Atom • Nucleus: Protons with positive charge + Neutrons with no Charge • Electrons: Move around the nucleus with negative charge • Number of electrons = Number of protons in an Atom. • Atom is always neutral
The Bohr Model of Atom and Photon Bohr’s Postulates: Stationary States: Electrons in certain orbit without radiation Atom radiates only when electron makes a transition from one to other state Frequency of the photon is given by hf = Ei-Ef
Elementary Particles Electron: Fundamental Subatomic Particle Mass (me) = 9.11x10-31 kg Charge (e) = -1.60 x 10-19 Coulomb or C Spin = 1/2
Proton and Neutron Proton: Fundamental Subatomic Particle Mass (mp) = 1.673x10-27 kg Charge (e) = 1.602 x 10-19 Coulomb or C Spin = 1/2 Neutron: Fundamental Subatomic Particle Mass (mn) = 1.675x10-27 kg Charge (e) = 0 Spin =1/2
Photon Charge = 0 Rest Mass = 0 Spin = 1 Speed of light in vacuum (c) = constant c = 2.99792458 x108 ~ 3 x 108 m/s
Electricity, Magnetism, Optics, Modern Physics Electrostatics: Interaction among charges Electricity and Magnetism : Movement of the charge particles Optics and Modern Physics: Interaction among electrons or atoms with photons
Two Important Elementary Particles Electron Photon
Electrostatics (Ch-20 &Ch-21) • Electric Charges and Forces • Charges, Atoms, and Molecules • Coulomb’s Law (Force between Charges) • The Concept of the Electric Field • Applications of the Electric Field • Conductors in Electric Fields • Forces and Torques on Charges in Electric Fields • Electric Potential Energy and the Electric Potential • Using the Electric Potential • Calculating the Electrical Potential • Sources of Electric Potential • Connecting Potential and Field • The Electrocardiogram • Capacitance and Capacitors • Dielectrics and Capacitors • Energy and Capacitors
What Will We Learn From Electrostatics? • Total charge in any system: Q • Electric Field at any point: E • Electric Potential at any point: V • Force between charges: F • Energy in any system: U
Chapter 20: Electric Charges, Forces and Fields • Electric Charges and Forces • Charges, Atoms, and Molecules • Coulomb’s Law (Force between Charges) • The Concept of the Electric Field • Applications of the Electric Field • Conductors in Electric Fields • Forces and Torques on Charges in Electric • Fields
Electric Charge Electron: Fundamental Subatomic Particle Mass (me) = 9.11x10-31 kg Charge (e) = -1.60 x 10-19 Coulomb or C Spin = 1/2
Discovering Electricity-I Expt-2 Expt-1 Expt-3 Repel each other Attract each other Nothing Happens
Discovering Electricity-II Expt-4 Two Charged Rods Expt-5 Expt-6 Both rods attract the paper Weakly attracted with wool Weakly repelled with Silk Greater forces with more rubbing Less forces with increasing distance
Charge Model I • Charging: Transfer of charge by rubbing or some other way • Two kinds of charge: Positive and negative • Like charges repel and opposite charges attract • Magnitude of force increases with the increase of charges and decreases with the increase of separation • Neutral objects have an equal number of positive and negative charges
Discovering Electricity-III Expt-7 Expt-8 Expt-9 Same charge as plastic Same charge as plastic One has charge and other does not Same charge as plastic Both have charges
Charge Model II 6. Two types of materials. Conductors and Insulators In conductors charges move easily and in Insulators charges are remain fixed in place 7. Charges can be transferred from one object to another by contact 8. Total charge in the universe is conserved: it can not be created or destroyed by any physical process
Visualization of charges 6. Two types of materials. Conductors and Insulators In conductors charges move easily and in Insulators charges are remain fixed in place 7. Charges can be transferred from one object to another by contact 8. Total charge in the universe is conserved: it can not be created or destroyed by any physical process
Charging by Induction (Polarization) Polarization Polarization induces opposite charges on the surface
Polarization: Applications Pulling water Attracting neutral object
Quantization of Charges Charge is quantized, occurring in “bits” of e, the magnitude of the fundamental charge on the electron or proton
Charges, Atoms, and Molecules Model View of an Atom
Forces between Charges( Coulomb’s Law) Coulomb’s Law
Comparison of Gravitational and Electrical Forces Forces between electron and proton in an atom
Forces in One Dimension If q1 = q2 , Then Fnet=0
Where do they collide? (a) Close to A (b) Close to B (c) At C
Superposition of Forces Determine a net force on a particular charge by all other charges
How does the net force compare? • The net force at A is • Less than at B • Greater than at B • Equal to at B -q charge is placed at either point A or B
Uniform Spherical Charge Distributions Can be treated as total charge of the sphere located at the center of the sphere