Electricity and Magnetism DC Circuits Using Kirchhoff s Laws

Transcription

1 Electricity and Magnetism DC Circuits Using Kirchhoff s Laws Lana Sheridan De Anza College Feb 9, 08

2 Last time power Kirchhoff s laws

3 Overview more Kirchhoff examples

4 Example with Two Batteries Find the current in the circuit. ure 8.4. ircuit. a e 6.0 V I b R 0 R 8.0 d e V ess at the e current ion of the s is repre- Suppose the current Figure flows 8.4 in the (Example direction shown. 8.6) A series circuit containing two t, but let s c

5 Example with Two Batteries wn in Figure 8.4. t in the circuit. a e 6.0 V I b R 0 R 8.0 and a guess at the two, so the current he direction of the rect guess is reprele circuit, but let s o junctions in this ts. d e V Figure 8.4 (Example 8.6) V = E IR E IR = 0 A series circuit containing two batteries and two resistors, where the polarities of the batteries are in opposition Traversing the circuit in the clockwise direcce of e, b S c represents a potential difference of c

6 Example with Two Batteries wn in Figure 8.4. t in the circuit. a e 6.0 V I b R 0 R 8.0 d e V Figure 8.4 (Example 8.6) V = E IR E IR = 0 and a guess at the two, so the current he direction of the rect guess is repre- A series circuit containing two le circuit, but let s batteries and two resistors, o junctions in this where the polarities of the batteries are in opposition. ts. I = E E = 0.33 A R + R 8.4. Traversing the circuit in the clockwise direcce of e, b S c represents a potential difference of Minus sign means that the current flows opposite to the direction shown in the diagram. c

7 batteries pation rate have in emfs (b) resistor V (4.0 and ) and (c) R R 6.0 V. What are (a) the current, the dissipation rate rate in (d) in battery (b) resistor and (4.0 (e) battery ) and (c)? Is + R resistor energy (8.0 being ), supplied and the or energy absorbed transfer by (f) + rate Page battery in (d) 76, battery and # (g) battery and (e)? battery? Is Fig. 7-5 energy In being Fig. supplied 7-6, the or ideal absorbed batteries by (f) Problem +. battery have emfs and (g) battery 50 V? and 50 V Q Fig. 7-5 and the resistances are R In Fig. 7-6, the ideal batteries 3.0 Problem R. and R have emfs.0.if the potential at P is 50 V and 50 V Q 00 V, what is it at Q? and the resistances are R R + and 3R ILW.0A.If car the battery potential with at a P is V R 00emf V, what and an is it internal at Q? resistance of P is being charged with a current of 50 3 ILW A car battery with a V A. What are (a) the potential difference V across the terminals, (b) the P Fig. 7-6 R Problem. emf and an internal resistance of is being charged with a current of 50 rate P A. What r of energy dissipation inside the are (a) the potential difference V across the terminals, (b) the Fig. battery, 7-6 and (c) Problem the rate. P emf of energy conversion to chemical form? When the battery is used to supply 50 A to the starter motor, what are (d) V and (e) P r? rate P r of energy dissipation inside the battery, and (c) the rate P emf of energy conversion to chemical form? When the battery is used to supply 50 A to the starter motor, what are (d) V and (e) P r? Using resistor Kirchhoff s (8.0 ), and Laws the energy examples transfer tric of t

8 batteries pation rate have in emfs (b) resistor V (4.0 and ) and (c) R R 6.0 V. What are (a) the current, the dissipation rate rate in (d) in battery (b) resistor and (4.0 (e) battery ) and (c)? Is + R resistor energy (8.0 being ), supplied and the or energy absorbed transfer by (f) + rate Page battery in (d) 76, battery and # (g) battery and (e)? battery? Is Fig. 7-5 energy In being Fig. supplied 7-6, the or ideal absorbed batteries by (f) Problem +. battery have emfs and (g) battery 50 V? and 50 V Q Fig. 7-5 and the resistances are R In Fig. 7-6, the ideal batteries 3.0 Problem R. and R have emfs.0.if the potential at P is 50 V and 50 V Q 00 V, what is it at Q? and the resistances are R R + and 3R ILW.0A.If car the battery potential with at a P is V R 00emf V, what and an is it internal at Q? resistance of P is being charged with a current of 50 3 ILW A car battery with a V A. What are (a) the potential difference Fig. 7-6 R Problem. emf and an internal resistance of P Loop is being rule: V across charged E the terminals, (b) the with IR a + current E IR of 50 = 0, I = 0 A. rate P A. What r of energy dissipation inside the are (a) the potential difference V across the terminals, (b) the Fig. battery, 7-6 and (c) Problem the rate. P emf Potential of energy atconversion Q = 0 to V. chemical form? When the battery is used to supply 50 A to the starter motor, what are (d) V and (e) P r? rate P r of energy dissipation inside the battery, and (c) the rate P emf of energy conversion to chemical form? When the battery is used to supply 50 A to the starter motor, what are (d) V and (e) P r? Using resistor Kirchhoff s (8.0 ), and Laws the energy examples transfer tric of t

9 Example with a Multiloop Circuit Find the currents I, I, and I 3 in the circuit. 4.0 V e f 4.0 I b 0.0 V 6.0 I c I (Example rcuit containing branches. a.0 d Suppose the currents flow in the direction shown. in Figure 8.5.

10 Example with a Multiloop Circuit Junction rule: I + I = I 3 () Loops: 0V (6Ω)I (Ω)I 3 = 0 () 4V + (6Ω)I 0V (4Ω)I = 0 (3) 4V (Ω)I 3 (4Ω)I = 0 (4)

11 Example with a Multiloop Circuit 4.0 V e f 4.0 I b 0.0 V 6.0 I c I 3 e 8.5 (Example A circuit containing ent branches. a.0 d ed in Figure 8.5. I = +.0 A I = 3.0 A I 3 =.0 A I I 3 5 0

12 Summary using Kirchhoff s Laws Next Test on Feb 5. Homework Collected homework, posted online, due on Monday, Feb. Serway & Jewett: PREVIOUS: Ch 8, onward from page 857. Problems: 5, 9, 5, 7, 3