II Circuit Basics Use these circuit diagrams to answer question 1. B C 1a. One of the four voltmeters will read 0. Put a checkmark beside it. b. One of the ammeters is improperly connected. Put a checkmark beside it. c. Still with the improperly connected ammeter what will it read? d. Circuit C has 2 voltmeters connected. Compare the readings on them. e. Circuit C which way are the electrons flowing (clockwise or otherwise?) f. Circuit C Compare the readings on the two ammeters. g. Circuit B add a wire (line) to the diagram to create a short circuit a path that allows the current to travel back to the battery without passing through a load. Potential Difference, and Resistance 2. Imagine you could actually see the flow of charge in a circuit electron Inside the resistor atoms a. dd an arrow to the diagram that shows the direction of electron flow. b. How how does the negative end of the battery differ from the positive end? c. Compare the number and speed of electrons moving into the resistor with those moving out of it. d. When electrons pass through the resistor they lose their electric potential energy and cause the resistor to heat up. Describe how this energy conversion takes place. e. Describe what an ammeter measures. f. Describe what a voltmeter measures. 3. The voltmeter in circuit B above reads 2.8, the ammeter reads 93.0 m. a. How many coulombs of charge flow through the resistor in 1.0 min.? b. How many electrons flow through the resistor in 1.0 s? c. Calculate the electric energy converted by the circuit in 1.0 min. 1
(m) Ohm s Law Students measured the current that resulted when a potential difference was applied to two different Ohmic resistors. The results of their work is graphed below. vs. Potential Difference 250 200 150 100 50 1. Calculate the resistance of both resistors. 0 0 0.2 0.4 0.6 0.8 1 1.2 Potential Difference () 2. What is it about the best fit lines that identifies the resistors as Ohmic? 3. dd a 3 rd line that could show a non-ohmic material. 4a. Students are attempting to set a DC power supply so that a mere 5.0 x 10 15 e - travel through a 20 Ω resistor every second. What potential difference will they require? b. How much energy does each electron convert when it passes through the resistor? Report your answer in both e and J. 5a. Fuses are used in electric circuits to shut off the current if there is a dangerous amount flowing. I was making a roast for my mom when a 15 fused blew in my stove at home. If the stove operates at 220 what was the maximum resistance in the stove element? b. What is the danger that results if too much current flows in a circuit? 6. How much current does a 2.00 kw electric fire (ha!) draw from the 230 mains? 7. transistor radio operates by means of a 9.0 battery that supplies it with 50 m of current. The battery has a useful life of 300 h and costs $1.79. a. What is the resistance of the radio circuitry? b. What total electric energy is provided by the battery during its useful life? c. What is the cost per joule of the energy? d. What is the cost per kilowatt-hour? 2
IIX Predicting Meter Readings 1. The diagrams below show seven circuits. ll of the batteries are identical, so are all the bulbs. Rank the ammeters, from the greatest current reading to the least. 1 2 3 4 5 6 7 Greatest Least Explain your reasoning: 2. Rank the ammeters from greatest current reading to least. 1 6 2 4 Greatest 3 5 Least Explain your reasoning: 3
3. Rank the ammeters. 2 1 5 6 3 7 4 8 9 Greatest Explain your reasoning: Least 4. Rank the ammeters. 1 2 7 4 6 3 5 Greatest Least Explain your reasoning: 4
IX Kirchhoff s Rules 1. Write the loop rule for this circuit. 2 2 3 3 t 1 1 2. Use the junction rule to complete these expressions (fill in the blank) for the parallel circuit below. t a It = I3 + + b. I5 = + c. I3 = It - 3 5 4 2 1 3. Write 2 loop rules for this circuit. 3 3 2 1 2 1 t t 4. a. ccording to the loop rule t = 2+4+ b. ccording to the junction rule I5 + = I3 c. Under what conditions can you predict that I1 = I2? 3 2 1 3 2 1 4 5 t 4 5 t 5
X Solving Circuits Determine the value of all meter readings for these circuits. 1 2 DC = 5.0 R = 3.0 R = 10.0 R = 6.0 = 20 3. = 3.0 R = 15.0 DC R = 10 4. R = 3.0 R = 3.0 R = 3.0 R = 6.0 = 20 5. 6. = 4.5 R = 3.0 R = 10 R = 20 R = 1.0 R = 2.0 = 12 6
7. Find the reading on all meters. R 2 = 2.0 R 3 = 2.0 T R 1 = 2.0 R 5 = 1.0 5 R 4 = 1.0 T I T = 1.0 6 R 6 = 3.0 8. a) Find the reading on all meters b) Calculate the value of R 4 c) Does conventional current flow clockwise or counter-clockwise in this circuit? R 1 = 20.0 2 2 = 5.00 T R 2 =50.0 R 4 T 4 R 3 = 12.0 3 3 = 3.6 9. 12.0 battery operates the circuit below. The resistors are R 1 = 5.0 ; R 2 = 10 ; R 3 = 20 ; R 4 = 5.0 ; R 5 = 2.5. Find all currents and voltages. 4 3 4 3 5 2 2 5 t 1 1 7
(m) XI Circuit Practice Quiz Use this diagram to answer questions 1 3 B T 3 2 R 1 = 5.0 E 1 1 a. There are two pairs of positions (labeled -E) you could connect the leads of a voltmeter and get a reading of 0. One is and C. What is the other pair? b. Name two points you could connect a voltmeter to get the same reading you get at the battery. 2. If we consider the current in the circuit to be conventional current to which position will it flow after it leaves point D? 3. Write 2 loop rules for this circuit. 4. Look at the shaded box to the right of point B. If you add a resistor at that position a. what will the effect be on the reading 3? (increased, decreased, unchanged) b. What will the effect be on the reading of t? (increased, decreased, unchanged) Use this graph to answer question 5 C R 2 = 5.0 D vs. Potential Difference R 3 = 5.0 80 70 60 50 40 30 20 10 0 0 0.5 1 1.5 2 2.5 3 Potential Difference () 5a. Calculate the slope of the graph and use it to determine the resistance of the device. b. How many electrons pass through the resistor in 1.0 min when a potential difference of 2.0 is applied to it? 8
6a. Determine the reading on all the meters in this circuit. = 3.0 R = 10 R = 20 6b. Determine the reading on all the meters in this circuit. = 9.0 R = 10 R = 20 2 1 7. My house used 197.80 kwh of electric energy during the last 30 days. a. How many joules of energy is this? b. Household power is used at about 115, so what average current did my house draw during these 30 days? 9
ppendix Page 1 1a. circuit b. circuit c. full scale deflection (max reading) d. they read the same value e. counterclockwise f. they read the same g. Or any other path that allows the current to make it back to the battery without traveling through the resistor. 2a. way from negative to positive b. There are more electrons at the negative end c. The flow of e- must be the same into and out of the resistor. d. The e- collide with atoms and increase the kinetic energy of the atoms = thermal energy. e. The number of electrons flowing through a circuit. f. The change in energy per unit of charge between two points in a circuit. 3a. 5.6 C b. 5.8 x 10 17 c. 16 J page 2 1. 5.0 Ω and 6.7 Ω 2. The lines are straight. 3. curved line. 4a. = 16 m b. 0.016 e or 2.6 x 10-21 J 5a. 15 Ω b. wires in the appliance or the home may overheat and cause a fire. 6. I = 8.7 7a. 180 Ω b. 4.9 x 10 5 J c. 0.037 /J d. $13/kW h Page 3 (lists separated by commas can occur in any order.) 1. 1, 2 3, 4, 5 6, 7 2. 1, 6 2, 3, 4, 5 Page 4 3. 6 5 1, 2, 3, 4, 7, 8, 9 4. 1 2 3, 4, 5, 6, 7 Page 5 Kirchhoff s Rules 1. t = 1 + 2 + 3 2.a I2 + I1 b. I2 + I1 c. I5 3. t = 1 + 3; and t = 2 + 3 4. a. 3 b. I4 c. both resistances are the same Page 6 Solving Circuits 1. I = 0.33 = 3.3 2. (ammeters from left to right) I = 6.7 I = 3.3 I = 10 = 20 3. (ammeters from left to right) I = 0.60 I = 1.2 I = 1.8 = 12 4. (ammeters from left to right) I = 6.7 I = 13.4 I = 20 I = 23.4 = 20 5. I = 1.1 10 = 1.5 20 = 3.0 10
5 = 4.5 6. 1 = 2.0 5 = 2.0 3 = 10 7. t = 3.2 I 5 = 0.52 6 = 0.52 8. t = 10.6 I t = 0.300 I 4 = 0.200 R4 = 35.0 9. t = 12.0 ; 3 = 9.6 ; 1 = 2 = 1.6 ; 4 = 5 = 0.8 I1 = I5 = 0.32 I2 = I4 = 0.16 I3 = 0.48 Page 8 - Practice Quiz 1 a. BE b. E, CE 2. C 3. a t = 1; t = 2 + 3; 1 = 2 + 3 4. a decreases b. unchanged 5. a. slope = 0.030 /; R = 33 Ω b. 2.3 x 10 19 6 a. I = 86 m; = 0.86 b. I1 = 0.77 ; = 5.1 ; I2 = 0.26 7. a 712.08 MJ b. 2.4 11