Electricity and Magnetismi. Recap: Electrostatic Forceii. Fundamental Forces cntd.Some Questions:Modern View (>1930)Strength of Electrostatic ForceFeb 8 2002Electricity and Magnetismi. i. Recap: Electric Charge and Electrostatic Forceii. Fundamental Forcesi. Strength and Range: Coulomb’s Lawiii. Electrostatic InductionFeb 8 2002i. Recap: Electrostatic Force• New Property of Matter: Electric charge–comes in two kinds: ‘+’and ‘-’–connected to a force• Electrostatic Force–attractive (for ‘+-’) or repulsive (‘--’, `++’)•Charge is conservedFeb 8 2002ii. Fundamental Forces cntd.• How does the Electric force compare to the other fundamental forces?•Gravity• Strong force (Atomic nuclei)• Weak force (Radioactivity, Star ‘fuel’)• How strong?• What Range?Feb 8 2002Strength10-710-20Weak ForceAtomsMoleculesElementary ParticlesEarthSolar SystemFarthest GalaxyStrong Force100Atomic Nuclei1015110-1510-1010-510510101Electric ForceHumanGravity 10-361020Feb 8 2002Some Questions:• What determines the range of the interaction?• How can one have ‘Action at a distance’?In-Class DemoFeb 8 2002Modern View (>1930)• Interactions ‘mediated’ by exchange of particles (‘gauge bosons’)– Weak interaction: Vector bosons (m large)– Strong interaction: Gluons (m=0)– Electric Force: Photons (m=0)– Gravity: Graviton (m=0)• For infinite range (e.g. Gravity,EM)– Exchanged particle must be massless!Feb 8 2002Strength of Electrostatic Force• How does it depend on charge?• How does it depend on distance?Charles Augustin de Coulomb(1736-1806)Coulomb’s Law
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