《Fundamentals of Physics精品教学-华南理工》27 Circuits.pptVIP

Fundamentals of Physics 27 Circuits 27-2 “Pumping” Charges DC circuit Fundamentals of Physics 27 Circuits 27-2 “Pumping” Charges Fundamentals of Physics 27 Circuits emf device: doing work on charge carriers, thus maintain a potential difference between terminals. (battery, electric generator, solar cell, fuel cell, physiological emf device) 27-2 “Pumping” Charges 27-3 Work, Energy, and Emf Fundamentals of Physics 27 Circuits Within emf device, positive charge carriers move from the negative terminal to the positive terminal. ideal emf device real emf device 27-3 Work, Energy, and Emf Fundamentals of Physics 27 Circuits 27-4 Calculating Current in a Single-Loop Circuit Fundamentals of Physics 27 Circuits Energy Method 27-4 Calculating Current in a Single-Loop Circuit Fundamentals of Physics 27 Circuits Potential Method Kirchhoff’s loop rule: The algebraic sum of the changes in potential encountered in a complete traversal of any loop of a circuit must be zero. Resistance rule: For a move through a resistor in the direction of the current, the change in potential is -iR. Emf rule: For a move through an ideal emf device in the direction of the emf arrow, the change in potential is +ε. 27-5 Other Single-Loop Circuits Fundamentals of Physics 27 Circuits Internal Resistance Resistances in Series 27-6 Potential Difference Between Two Points Fundamentals of Physics 27 Circuits From a to b through battery Or through resistor Potential Difference Across a Real Battery 27-6 Potential Difference Between Two Points Fundamentals of Physics 27 Circuits Grounding a Circuit Va=0 Vb=8.0 V Va=-8.0 V Vb=0 27-6 Potential Difference Between Two Points Fundamentals of Physics 27 Circuits Power, Potential, and Emf Fundamentals of Physics Sample Problem The emfs and resistances in the circuit have values: ε1=4.4 V, ε2=2.1 V, r1=2.3 Ω, r2=1.8 Ω, R=5.5 Ω. (a) What is the current in the circuit? (b) What is the potential difference between termin