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CHAPTER 16-17 • Electric Charge •Insulators vs. Conductors • Induced Charge •Coulomb’s Law • Solving Problems Involving Coulomb’s Law and Vectors • The Electric Field •Electric Potential Energy •Potential Difference The electric charge • Objects become charged by transferring electrons • Remove electrons → objects have positive charge • Add electrons → objects have electrons charge • Opposite charges Attract • Like Charges repel The electric charge • Electric Charge measured in COULOMBS. • A typical lightning bolt is only 15 C. • Charge of electron → 𝑞𝑒 = −1.602 ∗ 10 − 19 𝐶 • Rubbing a balloon on your head will transfer about CHARGING BY CONDUCTION Charging By Induction: No Direct contact. Coulombs Law Q1, Q2 = Electric Charge\ r = distance between charges + r=.25m 5μC + - r=.25m 5μC 5μC + +F → Charges are repelled 3μC r=.25m - 3μC - 3μC -F → Charges are attracted Coulombs Law • Principle of Superposition A + 0.30m B C 0.40m + 4μC 3μC FAB= 5μC FAC= FBC= FAB A FAC B FAB FBC FBC FAC C Coulombs Law • Principle of Superposition 2D A + 3μC Find the magnitude and direction of the Net Force on charge B 0.30m B FAB B + 4μC 0.40m 5μC C FBC FBC FAB The Electric Field • Area around a charge that exerts a force on other charges • Field Strength defined as Force per Unit Charge The Electric Field The Electric Field • Field Lines • The direction of an electric field can be determined based on the direction a positive charge would move • WWPCD WWEKD? The Electric Field A + 3μC 0.40m 0.30m E=? B 5μC The Electric Field A 6μC + Find the magnitude and direction of the Electric Field at the origin 0.40m E=? 0.50m 7μC B Electric Potential Energy • Potential Energy = ability of a force to do work. • Work can be done on an Electric Charge in an Electric Field. • 𝑊 = 𝐹𝑑 → 𝐸 = 𝐹 𝑞 → 𝐹 = 𝑞𝐸 → 𝑊 = 𝑞𝐸𝑑 = 𝑃𝐸 𝑃𝐸 = 𝑞𝐸𝑑 Electric Potential / Potential Difference • Electric potential = Defined as potential energy per unit charge. • Potential Difference = Work done per unit charge •𝑉= 𝑃𝐸 𝑞 •𝑉= 𝑃𝐸 𝑞 = 𝑊 𝑞 = 𝑞𝐸𝑑 𝑞 = 𝐽ൗ𝐶 = 𝑉𝑜𝑙𝑡 = 𝐸𝑑 𝑊 𝑉= = 𝐸𝑑 𝑞 Electric Potential / Potential Difference • Positive charges move from High Potential to Low Potential • (fall down) • Negative charges move from Low Potential to High Potential • (fall up) Electric Potential / Potential Difference Examples: • How much work is done moving a 5uC charge from zero potential to 12V of potential? • How strong is the electric field between to plates 7.0mm apart if the potential difference between them is 12V? New unit for electric field → 𝑉 = 𝐸𝑑 → 𝐸 = 𝐸 𝑑 = 𝑉Τ𝑚