PHYS 272 Matter and Interactions II Electric And

PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions http: //www. physics. purdue. edu/academic_programs/courses/phys 272/ PHYSICS 272 Electric & Magnetic Interactions Lecture 16 Electric Fields and Circuits [EMI Ch. 19] Fall 2010 Prof. Yong Chen (yongchen@purdue. edu) Prof. Michael Manfra (mmanfra@purdue. edu) Lec 16 Slide 1/24

PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions http: //www. physics. purdue. edu/academic_programs/courses/phys 272/ Remember this picture High V Low V What provides the E-field that drives electrons in wires in circuits? Fall 2010 Prof. Yong Chen (yongchen@purdue. edu) Prof. Michael Manfra (mmanfra@purdue. edu) Lec 16 Slide 2/24

PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions http: //www. physics. purdue. edu/academic_programs/courses/phys 272/ Field and current in a simple circuit Fall 2010 Prof. Yong Chen (yongchen@purdue. edu) Prof. Michael Manfra (mmanfra@purdue. edu) Lec 16 Slide 3/24

PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions http: //www. physics. purdue. edu/academic_programs/courses/phys 272/ Fall 2010 Prof. Yong Chen (yongchen@purdue. edu) Prof. Michael Manfra (mmanfra@purdue. edu) Lec 16 Slide 4/24

PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions http: //www. physics. purdue. edu/academic_programs/courses/phys 272/ Exercise: Fall 2010 Prof. Yong Chen (yongchen@purdue. edu) Prof. Michael Manfra (mmanfra@purdue. edu) Lec 16 Slide 5/24

PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions http: //www. physics. purdue. edu/academic_programs/courses/phys 272/ Clicker question 1: C Fall 2010 Prof. Yong Chen (yongchen@purdue. edu) Prof. Michael Manfra (mmanfra@purdue. edu) Lec 16 Slide 6/24

PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions http: //www. physics. purdue. edu/academic_programs/courses/phys 272/ Potential difference across connecting wires Connecting wires: thick copper wires Light bulb: resistive, low mobility Even for long connecting wires Therefore, the dominating energy dissipation is in the bulb. Fall 2010 Prof. Yong Chen (yongchen@purdue. edu) Prof. Michael Manfra (mmanfra@purdue. edu) Lec 16 Slide 7/24

PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions http: //www. physics. purdue. edu/academic_programs/courses/phys 272/ General use of the loop rule Fall 2010 Prof. Yong Chen (yongchen@purdue. edu) Prof. Michael Manfra (mmanfra@purdue. edu) Lec 16 Slide 8/24

PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions http: //www. physics. purdue. edu/academic_programs/courses/phys 272/ Two key principles Principle I: Charge conservation The Current Node Rule In the steady state, for many electrons flowing into and out of a node, electron current: net iin = net iout , where i = n. Au. E conventional current: net Iin = net Iout , where I = qn. Au. E Principle II: Energy conservation Energy Conservation (The Loop Rule) In the steady state, for any round-trip path, ∆V 1 + ∆V 2 + … = 0 Fall 2010 Prof. Yong Chen (yongchen@purdue. edu) Prof. Michael Manfra (mmanfra@purdue. edu) Lec 16 Slide 9/24

PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions http: //www. physics. purdue. edu/academic_programs/courses/phys 272/ Application 1: Thin filament bulb and thick filament bulb in series • Both bulb filaments are made of tungsten • The top, thin-filament bulb has small cross-sectional area • The bottom, thick-filament bulb has large cross section Current node rule: The loss of electric potential energy Kinetic energy of the electron Thermal energy and temperature of the wire Fall 2010 Prof. Yong Chen (yongchen@purdue. edu) Prof. Michael Manfra (mmanfra@purdue. edu) Lec 16 Slide 10/24

PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions http: //www. physics. purdue. edu/academic_programs/courses/phys 272/ Clicker Question 2 A) B) C) D) Fall 2010 Prof. Yong Chen (yongchen@purdue. edu) Prof. Michael Manfra (mmanfra@purdue. edu) Lec 16 Slide 11/24

PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions http: //www. physics. purdue. edu/academic_programs/courses/phys 272/ Clicker Question A) B) C) D) A Fall 2010 Prof. Yong Chen (yongchen@purdue. edu) Prof. Michael Manfra (mmanfra@purdue. edu) Lec 16 Slide 12/24

PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions http: //www. physics. purdue. edu/academic_programs/courses/phys 272/ Twice the Length Nichrome wire (resistive) Quantitative measurement of current with a compass Current is halved when increasing the length of the wire by a factor of 2. Fall 2010 Prof. Yong Chen (yongchen@purdue. edu) Prof. Michael Manfra (mmanfra@purdue. edu) Lec 16 Slide 13/24

PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions http: //www. physics. purdue. edu/academic_programs/courses/phys 272/ Doubling the Cross-Sectional Area Loop: emf - EL = 0 Electron current in the wire increases by a factor of two if the crosssectional area of the wire doubles. Nichrome wire Fall 2010 Prof. Yong Chen (yongchen@purdue. edu) Prof. Michael Manfra (mmanfra@purdue. edu) Lec 16 Slide 14/24

PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions http: //www. physics. purdue. edu/academic_programs/courses/phys 272/ Long and Round Bulb in Series only round bulb: The round bulb doesn’t light up! Fall 2010 Prof. Yong Chen (yongchen@purdue. edu) Prof. Michael Manfra (mmanfra@purdue. edu) Lec 16 Slide 15/24

PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions http: //www. physics. purdue. edu/academic_programs/courses/phys 272/ Why do we care these microscopic views? Moore’s law Small transistors: Single electron charge matters! Fall 2010 Prof. Yong Chen (yongchen@purdue. edu) Prof. Michael Manfra (mmanfra@purdue. edu) Lec 16 Slide 16/24

PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions http: //www. physics. purdue. edu/academic_programs/courses/phys 272/ Chapter 20: Circuit Elements Fall 2010 Prof. Yong Chen (yongchen@purdue. edu) Prof. Michael Manfra (mmanfra@purdue. edu) Lec 16 Slide 17/24

PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions http: //www. physics. purdue. edu/academic_programs/courses/phys 272/ Fall 2010 Prof. Yong Chen (yongchen@purdue. edu) Prof. Michael Manfra (mmanfra@purdue. edu) Lec 16 Slide 18/24

PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions http: //www. physics. purdue. edu/academic_programs/courses/phys 272/ Charging a capacitor After 0. 1 sec After many sec Fall 2010 Prof. Yong Chen (yongchen@purdue. edu) Prof. Michael Manfra (mmanfra@purdue. edu) Lec 16 Slide 19/24

PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions http: //www. physics. purdue. edu/academic_programs/courses/phys 272/ Discharging a capacitor After 0. 1 sec After many sec Fall 2010 Prof. Yong Chen (yongchen@purdue. edu) Prof. Michael Manfra (mmanfra@purdue. edu) Lec 16 Slide 20/24