* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Review Exam 4
Survey
Document related concepts
Electric battery wikipedia , lookup
Power electronics wikipedia , lookup
Superconductivity wikipedia , lookup
Operational amplifier wikipedia , lookup
Opto-isolator wikipedia , lookup
Thermal runaway wikipedia , lookup
Switched-mode power supply wikipedia , lookup
Surge protector wikipedia , lookup
Wien bridge oscillator wikipedia , lookup
Negative resistance wikipedia , lookup
Electrical ballast wikipedia , lookup
Lumped element model wikipedia , lookup
RLC circuit wikipedia , lookup
Two-port network wikipedia , lookup
Current source wikipedia , lookup
Power MOSFET wikipedia , lookup
Current mirror wikipedia , lookup
Rectiverter wikipedia , lookup
Transcript
Review Exam 4 Chapter 18 Electric Currents Resistance and Resistors The ratio of voltage to current is called the resistance: (18-2a) (18-2b) 18.4 Resistivity The constant ρ, the resistivity, is characteristic of the material. 18.4 Resistivity 18.4 Resistivity For any given material, the resistivity changes with temperature: Since R T R 0 1 T - T0 R0 = Resistance at some reference temperature (T0) α = temperature coefficient and R = resistance at some new temperature T If positive, if T , R If negative if T , R 18.5 Electric Power 18.5 Electric Power The unit of power is the watt, W. 1Watt = 1 Joule/second Chapter 19 DC Circuits Conservation Laws • Conservation of Charge (I = Q/t) and I • Conservation of Energy (PE = QV) and V • Conservative Forces (pages 148-149) • ∑ of Work around a closed path = 0 • Independent of Path • For a closed loop ∑ of PE gained and lost or ∑ of V gained and lost = 0 I ε + - ε-V = 0 ε –IR =0 ε = IR Simple Circuit R V = IR Resistors in Series From this we get the equivalent resistance (that single resistance that gives the same current in the circuit). Resistors in Parallel This gives the reciprocal of the equivalent resistance: (19-4) Repeat this Mantra • The current is the same for elements connected in series • The voltage is the same for elements connected in parallel Multiple Loop Game Rules • Draw picture • Define number of loops • Pick ARBITRARY directions for the currents • Indentify branch points (where currents divide) • Currents into branch points = currents out of branch points • Circle each loop and ∑ V’s = 0 How to circle a loop • Start at some ARBITRARY point • Circle clockwise or counterclockwise (your choice) • End at starting point How to Add V’s When you come to a Battery as you circle the loop ε -ε Direction you take +ε When you come to a Resistor as you circle the loop you will travel with or against the current R I - IR + IR 19.5 Circuits Containing Capacitors in Series and in Parallel In this case, the total capacitance is the sum: (19-5) 19.5 Circuits Containing Capacitors in Series and in Parallel In this case, the reciprocals of the capacitances add to give the reciprocal of the equivalent capacitance: (19-6) Ammeters – Very small resistance so voltage across it is very small In series Voltmeters - Very large resistance, takes away little current. In Parallel What would happen if I put an Ammeter in Parallel? A ConcepTest 19.8 Kirchhoff’s Rules The lightbulbs in the 1) both bulbs go out circuit are identical. When 2) intensity of both bulbs increases the switch is closed, what 3) intensity of both bulbs decreases happens? 4) A gets brighter and B gets dimmer 5) nothing changes ConcepTest 19.8 Kirchhoff’s Rules The lightbulbs in the 1) both bulbs go out circuit are identical. When 2) intensity of both bulbs increases the switch is closed, what 3) intensity of both bulbs decreases happens? 4) A gets brighter and B gets dimmer 5) nothing changes When the switch is open, the point between the bulbs is at 12 V. But so is the point between the batteries. If there is no potential difference, then no current will flow once the switch is closed!! Thus, nothing changes. Follow-up: What happens if the bottom battery is replaced by a 24 V battery? 24 V ConcepTest 19.10 More Kirchhoff’s Rules 1) 2 – I1 – 2I2 = 0 Which of the equations is valid 2) 2 – 2I1 – 2I2 – 4I3 = 0 for the circuit below? 3) 2 – I1 – 4 – 2I2 = 0 4) I3 – 4 – 2I2 + 6 = 0 5) 2 – I1 – 3I3 – 6 = 0 1 I2 2 6V 22 VV 4V I1 1 I3 3 ConcepTest 19.10 More Kirchhoff’s Rules 1) 2 – I1 – 2I2 = 0 Which of the equations is valid 2) 2 – 2I1 – 2I2 – 4I3 = 0 for the circuit below? 3) 2 – I1 – 4 – 2I2 = 0 4) I3 – 4 – 2I2 + 6 = 0 5) 2 – I1 – 3I3 – 6 = 0 Eqn. 3 is valid for the left loop: The left battery gives +2V, then there is a drop through a 1 resistor with current I1 flowing. Then we go through the middle battery (but from + to – !), which gives –4V. Finally, there is a drop through a 2 resistor with current I2. 1 I2 2 6V 22 VV 4V I1 1 I3 3