Transcript Physics 123
Physics 223 28. Direct Current (DC) Circuits 28.1 EMF and Voltage 28.2 Resistors in Series and Parallel 28.3 Kirchhoff’s Rules 28.4 RC Circuit 28.5 Ammeters and Voltmeters 28.6 Household Wiring Electric Battery + - The battery converts chemical energy to electrical energy. It is a source of potential difference or voltage. This is used to drive electrons “downhill” through a conductor (resistor) Electric Current and Ohm’s Law I=Q/t V=IR current = charge / time voltage = current x resistance 28.1 EMF and Voltage V= ɛ-Ir r is the “hidden” internal resistance of the battery. 28.2 Bulbs in Series and Parallel L3 L1 L2 L4 A. B. C. D. L1 and L2 are in series L1 and L2 are in parallel L3 and L4 are in series None of the above Bulbs in Series and Parallel L3 L1 L2 L4 L1 and L2 are in series and L3 and L4 are in parallel Bulbs in Series and Parallel L3 L1 L2 L4 A. B. C. D. I1 = I 2 V1 = V2 I3 = I 4 None of the above Bulbs in Series and Parallel L3 L1 L2 L4 Series I1 = I 2 Parallel V3 = V 4 Example 28.1 . . . Series Circuit R1 = 3Ω R2 = 6Ω V = 12V Calculate the current flowing through the resistors voltage across the resistors power dissipation in the resistors Solution 28.1 . . . Series Circuit R1 = 3Ω R2 = 6Ω V = 12V Req = 9Ω V = 12V Req = R1 + R2 I = 12/9 =4/3 A V1 = 4/3 x 3 = 4 V V2 = 4/3 x 6 = 8 V Example 28.2 . . . Parallel Circuit R1 =6 Ω R2 = 3 Ω 12V Calculate the current flowing through the resistors voltage across the resistors power dissipation in the resistors Solution 28.2 . . . Parallel Circuit R1 =6 Ω Req =2Ω R2 = 3 Ω 12V V = 12V 1/ Req = 1/R1 + 1/R2 I1 = 12/6 =2 A I2 = 12/3 =4 A Example 28.3 . . . Series /Parallel Combo Special! R2 =6Ω R3 =4Ω R1 =3Ω V =12V Calculate the current flowing through the resistors voltage across the resistors power dissipation in the resistors Solution 28.3 . . . Series /Parallel Combo Special! R2 =6Ω R3 =4Ω Req =2Ω R3 =4Ω R1 =3Ω V =12V Ieq = 12/6 =2A Veq = 2 x2 = 4V V1 = V2 = 4V I1 = 4/3 A and I2 = 2/3 A V =12V 28.3 Kirchhoff’s Rules I = 0 (Junction) V = 0 (Loop) RC Charging Circuit V0 VR VC VC = V0 (1 - e -t /RC ) VR = V0 e -t /RC t RC Discharging Circuit VR =VC VC = V0 e -t /RC VR = V0 e -t /RC t 28.5 Ammeters and Voltmeters V A Voltmeter measures voltage Ammeter measures current Voltmeter is connected in parallel Ammeter is connected in series Voltmeter has a HIGH resistance Ammeter has a LOW resistance Voltmeter is easy to hook up Ammeter is tricky to hook up That’s all folks!