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Midterm

# PY 212 Midterm: PY 212 Test 1 Material Summary

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Department
Physics
Course
PY 212
Professor
Heyward
Semester
Spring

Description
Chapter 18 Summary Charge behavior: • Net charge is conserved. • Electronsmovein solids,not protons. • Like charges repel; oppositecharges attract. • Neutral objectsare attractedto both positiveand negative charges because of polarization. • Net charge mustbe in multiplesof ‘e’. • Charge by contact;charge by induction. Insulators& Conductors: • Charges don’tflow on insulators. Charges do flow on conductors. • Both polarize but in different ways. • Understandbehavior when charged insulatorsand conductorscomeinto contactwith each other. 𝑞1 2 • Valid for point charges only. 𝐹𝑒𝑙 = 𝑘 𝑟 2 • Obeys superposition. • Valid for point charges only. 𝑞 • Obeys superposition. 𝐸 𝑝𝑜𝑖𝑛𝑡 𝑐ℎ𝑔 = 𝑘 𝑟2 • Pointsaway from positivecharges and towardnegative charges. • The dielectric strengthof air = 3e6 N/C. • This is a general equation (always true) 𝐹 𝑒𝑙𝑞𝑜𝐸 • q os the objectcharge. • F and E pointin the samedirectionfor positive qo, and oppositedirectionsfor negativeoq . • Forcesand electric fields obey superposition. E-field Lines: • Run from positiveto negative charges (unless go to infinity). • The directionof the E-field is tangentto the E-field line. • The magnitudeof the E-field is proportionalto the densityof the E-field lines. • The number of lines goinginto or out of an object is proportionalto the magnitudeof the charge. • They cannotcross. • For a uniform E-field, the E-field lines are parallel and equally spaced. • Know how to draw E-field lines for isolatedcharges and for an electric dipole. Conductorsin ElectrostaticEquilibrium: • The E-field inside is zero. • Excesscharges moveto the surface. • E-fields just outsidea conductorare perpendicular to its surface. • Charges are more concentratedat bends. • E-fields just outsidea conductorare greater at bends. • Electric potentialis the same everywhere in and on a conductorin staticequilibrium. Uniformly Charged Sphere: • The E-field inside is zero. • The E-field outsideis the same as a pointcharge. • Electric potentialis the same everywhere inside. • The electric potent
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