Fundamentals of Physics 8/e 26 - Ohm'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 26-1 What Is Physics? 26-2 Electric Current 26-3 Current Density 26-4 Resistance and Resistivity 26-5 Ohm’s Law 26-6 A Microscopic View of Ohm’s Law 26-7 Power in Electric Circuits 26-8 Semiconductors 26-9 Superconductors 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 26-1 What Is Physics? In this and the next chapter, we discuss the physics of electric currents —that is, charges in motion. 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 26-2 Electric Current A B i + q conductor i - q conductor Current = rate at which charge flows Current SI Unit: C/s known as the “Ampere” 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 26-3 Current Density i + q conductor A i - q conductor A SI unit for J: A/m² i = JA i0= i₁+i₂ 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 26-3 Current Density 彰化師大教學卓越－普物教材－理學院長郭艷光主持

26-4 Resistance and Resistivity + - i V If we apply a voltage V across a conductor a current i will flow through the conductor. We defined the conductor resistance as the ratio. SI Unit for R: V /i = the Ohm (symbol Ω) R + - i V 彰化師大教學卓越－普物教材－理學院長郭艷光主持

26-4 Resistance and Resistivity 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 26-5 Ohm’s Law The current i through a conductor is proportional to the voltage V applied across it. Not all conductors abey Ohm’s law (these are known as “non-Ohmic”) Note: Ohm’s “law” is in reality a definition of Ohmic conductors (defined as the conductors that obey Ohm’s law) 彰化師大教學卓越－普物教材－理學院長郭艷光主持

26-6 A Microscopic View of Ohm’s Law 彰化師大教學卓越－普物教材－理學院長郭艷光主持

26-7 Power in Electric Circuits SI unit for P: V‧A It is known as the “Watt”(symbol W). For Ohmic conductors: 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 26-8 Semiconductors Property Unit Copper Silicon Type of material Metal Semiconductor Charge carrier density m3 8.49×1028 1×1016 Resistivity Ω·m 1.69×108 2.5×103 Temperature coefficient of resistivity K－1 4.3× 103 －70 × 103 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 26-9 Superconductors In 1911, Dutch physicist Kamerlingh Onnes discovered that the resistivity of mercury absolutely disappears at temperatures below about 4 K. This phenomenon of superconductivity is of vast potential importance in technology because it means that charge can flow through a superconducting conductor without losing its energy to thermal energy. 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 26! 彰化師大教學卓越－普物教材－理學院長郭艷光主持