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Transcript
Reading Quiz 1. What is the SI unit of charge? 2. A charge alters the space around it. What is this alteration of space called? A.Coulomb B. Faraday C. Ampere D. Ohm E. Volt A.Charged plasma B. Charge sphere C. Electric ether D. Electric field E. Electrophoresys 3. If a negative charged rod is held near a neutral metal ball, the ball is attracted to the rod. This happens 4. The electric field of a charge is defined by the force on A. because of magnetic effects. B. because the ball tries to pull the rod’s electrons over to it. C. because the rod polarizes the metal. D. because the rod and the ball have opposite charges. A.an electron. B. a proton. C. a source charge. D. a test charge. What is the SI unit of charge? A. Coulomb B. Faraday C. Ampere D. Ohm E. Volt A charge alters the space around it. What is this alteration of space called? A. Charged plasma B. Charge sphere C. Electric ether D. Electric field E. Electrophoresys If a negative charged rod is held near a neutral metal ball, the ball is attracted to the rod. This happens A. because of magnetic effects. B. because the ball tries to pull the rod’s electrons over to it. C. because the rod polarizes the metal. D. because the rod and the ball have opposite charges. The electric field of a charge is defined by the force on A. an electron. B. a proton. C. a source charge. D. a test charge. The Electric Dipole Coulomb’s Law - Magnitude K q1q2 Fe 2 r • K = 9.0 x 109 N m2/C2 – Coulomb’s contant • q1, q2 = charges – measured in Coulombs (C) – 1 C is a lot of charge! • r = distance between q1 and q2 q1q2 Fe 2 40 r 1 ε0 =permittivity of free space (more relevant to future chapters) Electric Force K q1q2 Gm1m2 Fg Fe 2 2 r r • Similar form as gravitational force (weird, huh?), except – positive and negative charges • Like charges repel; opposite charge attract Net Force from Multiple Charges • An electrostatic force exists between each pair of charges according to Coulomb’s law k q1q2 k q1q3 k q2q3 Fe Fe,12 Fe,13 Fe,23 2 2 2 r r r • Add components of forces to get net force when adding multiple charges The Electric Field We begin our investigation of electric fields by postulating a field model that describes how charges interact: 1.Some charges, which we will call the source charges, alter the space around them by creating an electric field. 2.A separate charge in the electric field experiences a force exerted by the field. Suppose probe charge q experiences an electric force Fon q due to other charges. The units of the electric field are N/C. The magnitude E of the electric field is called the electric field strength. The Electric Field Group Problems Group Problems • Workbook Volume 4 • Pages 26-9 – 26-12 Group Problems 1. What is the net force on the 48 C charge? Field? Q1 Q2 +y +x Q4 Q3 2. Find net force on Q1. Field?