Phy107Spr07Lect35

Phy107Spr07Lect35 - Essa y d u e n e x t w e e k W e d M a y 2 Particles and fields M o d e rn v ie w is t h a t p a rt ic le s fie ld s a n d fo

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1 Wed. Apr. 25, 2007 Phy107 Lect. 35 1 Particles and fields • We have talked about several particles – Electron, photon, proton, neutron, quark • Many particles have internal constituents – Not fundamental: proton and neutron • We have talked about various forces – Electromagnetic, strong, weak, and gravity • And some fields… – Electric field – Magnetic field Today: more fields and more particles! Essay due next week Wed., May 2 Wed. Apr. 25, 2007 Phy107 Lect. 35 2 • Modern view is that particles, fields, and forces are intertwined. • The electromagnetic field is quantized. • It can be in many different energy states Ground state (lowest energy) First excited state (next highest energy) Wed. Apr. 25, 2007 Phy107 Lect. 35 3 Interactions between charges The positively charged rod attracts negative charges to the top of the electroscope. This leaves positive charges on the leaves. The like-charges on the leaves repel each other. attractive force between positive and negative charges. repulsive force between two positive or two negative charge Why did the electrons flow? Wed. Apr. 25, 2007 Phy107 Lect. 35 4 Force between charges Opposite charges attract Like charges repel. Other than the polarity, they interact much like masses interact gravitationally. Force is along the line joining the particles. Gravitational force : F G =GM 1 M 2 / r 2 G =6.7x10 -11 Nm 2 / kg 2 Electrostatic force: F E = k Q 1 Q 2 / r 2 k = 9x10 9 Nm 2 /C 2 + Force on positive particle due to negative particle Wed. Apr. 25, 2007 Phy107 Lect. 35 5 Electric field lines • Faraday invented the idea of field lines following the force to visualize the electric field. Field lines emanate from positive charge and terminate on negative charge. Local electric field is same direction as field lines. Force is parallel or antiparallel to field lines. Charged particle will move along these field lines. Wed. Apr. 25, 2007 Phy107 Lect. 35 6 Magnetism: Permanent magnets • North Pole and South Pole This is the elementary magnetic particle Called magnetic dipole (North pole and south pole) There are no magnetic ‘charges’ N S N S N S S N Likes attract Unlikes repel
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2 Wed. Apr. 25, 2007 Phy107 Lect. 35 7 Field lines of a magnet
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This note was uploaded on 01/05/2012 for the course PHYS 107 taught by Professor N/a during the Spring '08 term at Wisconsin.

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Phy107Spr07Lect35 - Essa y d u e n e x t w e e k W e d M a y 2 Particles and fields M o d e rn v ie w is t h a t p a rt ic le s fie ld s a n d fo

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