Fundamentals of Physics 8/e 21 - Coulomb's Law D. Halliday, R. Resnick, and J. Walker 國立彰化師大教學卓越計畫 理學院普通物理整合型教材 主持人：郭艷光院長

彰化師大教學卓越－普物教材－理學院長郭艷光主持 Outline 21-1 What Is Physics? 21-2 Electric Charge 21-3 Conductors and Insulators 21-4 Coulomb’s Law 21-5 Charge Is Quantized 21-6 Charge Is Conserved 彰化師大教學卓越－普物教材－理學院長郭艷光主持

彰化師大教學卓越－普物教材－理學院長郭艷光主持 21-1 What Is Physics? In this chapter we will introduce a new property of matter known as “electric charge” (symbol q). 彰化師大教學卓越－普物教材－理學院長郭艷光主持

彰化師大教學卓越－普物教材－理學院長郭艷光主持 21-2 Electric Charge Charges of the same sign repel each other. Charges of opposite sign attract each other. 彰化師大教學卓越－普物教材－理學院長郭艷光主持

21-3 Conductors and Insulators + Conductors are materials that allow charges to move freely through them. Examples are: copper, aluminum, mercury. Insulators are materials through which charges cannot move freely. Examples are: plastic, rubber, glass, ceramics. 彰化師大教學卓越－普物教材－理學院長郭艷光主持

彰化師大教學卓越－普物教材－理學院長郭艷光主持 21-4 Coulomb’s Law 彰化師大教學卓越－普物教材－理學院長郭艷光主持

彰化師大教學卓越－普物教材－理學院長郭艷光主持 21-4 Coulomb’s Law 彰化師大教學卓越－普物教材－理學院長郭艷光主持

彰化師大教學卓越－普物教材－理學院長郭艷光主持 21-4 Coulomb’s Law Q2 Q1 Q1 Q2 r F1 m1 m2 r F m2 m1 彰化師大教學卓越－普物教材－理學院長郭艷光主持

彰化師大教學卓越－普物教材－理學院長郭艷光主持 21-5 Charge Is Quantized Ne Np Nn Mass and charge of atomic constituents Neutron (n): Mass m = 1.67510-27 kg ; Charge q = 0 Proton (p): Mass m = 1.67310-27 kg ; Charge q = +1.60210-19 C Electron (e): Mass m = 9.1110-31 kg ; Charge q = -1.60210-19 C Note 1: We use the symbol “-e” and “+e” for the electron and proton charge, respectively. This is known as the elementary charge Note 2: Atoms are electrically neutral. The number of electrons is equal to the number of protons. This number is known as “ atomic number ” (symbol: Z) The chemical properties of atoms are determined exclusively by Z. Note 3: The sum of the number of protons and the number of neutrons is known as the “ mass number ” (symbol: A) Notation: Z = 92 = number of protons/electrons A = 235 = number of protons + neutrons 彰化師大教學卓越－普物教材－理學院長郭艷光主持

彰化師大教學卓越－普物教材－理學院長郭艷光主持 21-6 Charge Is Conserved silk glass rod silk glass rod - + 彰化師大教學卓越－普物教材－理學院長郭艷光主持

彰化師大教學卓越－普物教材－理學院長郭艷光主持 End of chapter 21! 彰化師大教學卓越－普物教材－理學院長郭艷光主持