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Unit 7 Lesson 1 Exercises 1. If 2.0 A of current flow through a lightbulb for 20. minutes. a) how many coulombs of charge (Q) have flowed thru the bulb? b) how many electrons (N) have moved through the lamp? (2400 C; 1.5 ×1022 electrons) 2. Find the current and direction 120 V 20 Ω (6A, CW) 3. If this circuit is connected for 60. minutes, find a) the current (I) b) the total charge flow through the circuit (Q) c) the # of electrons that have flowed through the circuit (N) 120 V 60. Ω (2.0A, 7200C, 4.5×1022) 4. A student uses a variable voltage power supply and connects it to a lab resistor. The student uses a voltmeter and an ammeter to measure the voltage drop across the resistor and the current through it. resistor power supply battery cell a) show on the diagram above how you would connect the meters to this circuit b) plot the following data taken by the student and use it to find the resistance of the resistor current through resistor (amp) voltage drop across resistor (volt) 0.00 0.0 0.80 2.0 1.90 4.0 2.70 6.0 3.70 8.0 4.50 10.0 Physics 12 Student Workbook ©Donald J. Mathewson 2002 429 5. In a house circuit, take the voltage to be 120 volts. Find the current if we plug in a) a 240 ohm light bulb b) a 12 ohm hair dryer c) a 20. ohm microwave d) a 0.10 ohm wet finger (0.50 A; 10. A; 6.0 A; 1200 A) 6. The circuit breakers in your house are designed to 'break' the circuit if the current gets too large. Most circuit breakers are set to 'break' or 'trip' at 15 A. If the house voltage is 120 volts, what is the minimum resistance of an appliance? (8.0 Ω ) 7. Why is it important to have circuit breakers (or fuses) for the circuits in our house? Explain using relevant principles of physics. 8. Find the force (and direction) on the positive charge below. 15.0 cm -1.00 µ C 10.0 cm +3.00 µ C -1.00 µ C (3.13 N West) 9. Find the work done in moving the 2.5 µC charge from the - plate to the + plate. (4.4 × 10-4 J= 0.44 mJ) 175 V +++++++++++++++++++++++++++++++++++++++++++ 7.50 cm 175 V 0V 2.5 µ C + -------------------------------------------0V 10. Find the angle of the conical pendulum if the 2.5 kg mass completes a 2.0 metre radius circle in 1.25 seconds.(79°) Physics 12 Student Workbook ©Donald J. Mathewson 2002 430 Unit 7 Lesson 2 Exercises 1. A 120 V source is connected to a 300. W resistor. Find a) the current b) the resistance c) the heat energy produced in 20. minutes 120 V 300. W (2.5A; 48 Ω ; 3.6×105J or 0.10 kWhr) 2. A 120. V source is connected to a 1500. W kettle. Find a) the current b) the resistance c) the energy (in kWhr) used in a day d) if energy costs 5.20 cents per kWhr, how much would it cost to run the kettle for a day (12.5 A; 9.60Ω ; 36.0 kWhr; $1.87) 3. A 1500 Watt kettle produces 2000. J of heat energy in 30. seconds. Find its efficiency (4.4%) 4. A bulb is connected to a power supply which is turned on. The current thru the bulb is measured to be 0.450 A and the voltage is measured to be 4.40 volts. The bulb is found to produce 1.50 J/s of light and heat energy. Find the bulb's efficiency ( 75.8%) 5. A 220. Watt computer is connected to 110. volts of alternating current and left on all month. Find a) the resistance b) current c) energy used per 30 day month d) cost of electricity (5.50 cents/ kWhr) (55.0Ω ;2.00A; 158 kWhr; $8.71) 6. A 100.% efficient electric motor runs on 11.0A and 110. V. At what speed could the motor pull a)10 kg mass straight up (12.3 m/s) ` b) 80 kg mass up a frictionless 15° ramp (5.96 m/s) motor 10kg motor 80 kg 15° 7. It takes 10.0 kJ of energy to cook a hot dog. If a 30.0 ohm hot dog is connected to 120. volts, how long will it take until it is cooked? (20.8 sec) Physics 12 Student Workbook ©Donald J. Mathewson 2002 436 8. Find the work done (energy required) in launching a 12 100 kg satellite from the surface of the Earth to a circular orbit 10 200 km above the surface of the Earth. (6.11 × 1011 J) 9. A 1000. kg car has a maximum power output of 100. horse-power (1 hp = 746 Watt). How steep a hill can it climb at constant speed of 60. km/hr if frictional forces add up to 500. N? (24°) 10. Find the work done and the speed after 6.00 metres of displacement (starting from rest) (3.00 × 102 J; 11.0 m/s) top view, 5.00 kg mass on frictionless table 30.0 N 5.00 kg 40.0 N 11. A 2.00 kg pendulum (1.75 metre long) is released from a 40.0° angle a) if there is no friction, find its speed at the bottom (2.83 m/s) b) if its speed at the bottom is 2.20 m/s, find the energy lost due to friction/heat energy created (3.18 J) 40.0° released from rest 12. A cliff jumper of mass 55.0 kg jumps off a 25.0 metre high cliff. After falling for 2.00 seconds, find (using h=0 at the bottom of the cliff) a) the kinetic energy (10.6 kJ=1.06 × 104J) b) the potential energy (2.91 kJ=2.91 × 103 J) 13. A 5.00 kg mass moving at 2.25 m/s East hits and sticks to a 8.00 kg mass moving North at 2.00 m/s. The collision lasts 0.250 seconds. Find a) the final speed and direction of the two masses (1.50 m/s 54.9° NofE) b) draw a momentum vector triangle showing Pi=Pf c) find the collision force on the 5 kg mass (37.1 N at 41.6° NofW) 14. A 10.0 kg hammer intially at rest free falls for 2.0 metres and then hits a 2.00 kg peg. Assume the peg and hammer move together freely after the collision, and that the collision takes 0.0250 seconds. Find a) their speed after the impact. (5.22 m/s) b) the collision force (418 N) Physics 12 Student Workbook ©Donald J. Mathewson 2002 437 Unit 7 Lesson 3 exercises: find unknown voltages and currents 1. 80 V drop V drop = 240 V gain 60 V drop 2. (100V) 12.5 A 2.5 A I= 4 A (6 A) 3. 12 V 18 V V= 20 V 4. (50V) I= 1 A 2 A (3A) 5. The three bulbs below are identical- which bulb is brightest? Explain your answer. i) bulb A ii) bulb B iii) bulb C iv) equally bright Note that bulb brightness depends on power, and therefore on both current and voltage drop A 10 V Physics 12 Student Workbook ©Donald J. Mathewson 2002 B C 447 6. Find unknown voltages and currents V= I= 100 V V= I= R=50 OHM R= 10 OHM V= I= 10 OHM 1A V= V= I= R=50 OHM note: two identical resistors in parallel will split the current evenly (40V 2A 20 OHM; 50V 1A; 50V 1A; 10V 1A; 10V) 7. Find unknown voltages and currents 4A V= 2A 4V V= I= 12 V I= (4A; 8V; 4V 2A) 8.Find unknown voltages and currents 6V 2A 9A V= (6V; 6V 3A; 6V) 4A V= V= I= 9. Find unknown voltages and currents 6V 6A I= V= I= 2A V= 3V I= (13V 6A; 6A; 4A 4V) 4V Physics 12 Student Workbook ©Donald J. Mathewson 2002 448 10. Find unknown voltages and currents 2V I= I= V=55 I= 2A V= V= 10V 5A (7A; 7A; 10V; 3A 43V; 43V) 4A V= 11. Find unknown voltages and currents (1A; 20V; 5V 1A; 1A 55 OHM 55V) 20 OHM 1A V= 5 OHM V= I= 80 V I= R= V= I= 12. Find unknown voltages and currents 20 OHM I=3A V= 120 V I= V= I= R= V= I=2A R= (5A; 60 V; 60V 3A 20 OHM; 120 V 60 OHM) 13. Find unknown voltages and currents 20 OHM V= I= 10 OHM I=1A V= 5 OHM 6A V= 15 OHM V= I= note: in problesm such as these, assume that the two end wires are connected to a cell. that has not been shown (20V 1A; 10V; 30V; 105V 7A) Physics 12 Student Workbook ©Donald J. Mathewson 2002 449 14. What can be said about the currents I1 and I 2 if the resistance of R 2 is half the resistance of R 1? I2 I1 R 10 V R/2 explain your answer using appropriate physics principles 15. What can be said about the voltage drops V1 and V2 if the resistance of R 1 is three times the resistance of R 2? 3R V1 V R V2 explain your answer using appropriate physics principles 16. What can be said about the resistances R1 and R 2 if the current through R 2 is three times the current through R 1? 10 V I 3I R1 R2 explain your answer using appropriate physics principles Physics 12 Student Workbook ©Donald J. Mathewson 2002 450 Unit 7 Lesson 4 Exercises 1. Find all unknown voltages and currents(2.5 A,15V; 2.5A, 25V; 2.5 A, 20. V) 6.0 Ω 10.0 Ω 60. V 8.0 Ω 2. Find all unknown voltages and currents (6.0 A,12 V; 6.0 A, 48 V; 6.0 A,60. V) 2.0 Ω 8.0 Ω 120 V 10.0 Ω 3. Find all unknown voltages, currents and resistances (5.0 Ω , 40. V; 8.0 A, 2.5 Ω ; 8.0 A, 40 V) 8.0 A 100. V 20. V 5.0 Ω 4. Which resistors are in series? R1 R5 R6 R7 R8 R2 R3 R4 5) For the circuit in question 4, complete the equations: I 3 = ___a________ V 2 = ____b___________ I 1 =__c_________ V t = V1 + V3 + _d______ I5 = I 6 + ____e____ I 7 = ___f______ V 6 = _____g________ (a)I 4;(b) V3+V4;(c) I 2+I 3 or I 2+I 4; (d)V4; (e) I 7 or I 8; (f) I 8; (g) V7 + V8 Physics 12 Student Workbook ©Donald J. Mathewson 2002 456 6. Find all voltage drops and currents (120 V, 12A; 120V,8.0A;120V,4.0A) 30. Ω 10. Ω 15 Ω 120 V 7. Find the total current in #6 if we a) remove the 15 ohm b) remove the 30. ohm c) add another 10. ohm in parallel d) add a 120 ohm in parallel (16A) (20. A) (36 A) (25 A) 8. Find all voltage drops and currents (120. V,0.833 A;120.V, 6.67 A; 120. V,1.67 A) 200. Watt 100. Watt 800. Watt 120. V light blender microwave 9. i) In household circuit #8, find the total current if we make the following changes to the circuit. ii) Indicate as well if these changes would cause the circuit breaker to trip(this happens when the total current exceeds 15.0 A) a) adding another 100. W light (in parallel) b) removing the 800. W microwave c) adding a 1400. W hair dryer (in parallel) d) adding a 300. W computer (in parallel) (no I t =10.0 A) (no I t =2.50 A ) (yes I t = 20.8 A) (no I t = 11.7 A) 10. What is the maximum number of the following in a house circuit a) 100 W light bulbs b) 250 W TV's b) 10 W toothbrushes d) 800 W toasters (18; 7;180; 2) Physics 12 Student Workbook ©Donald J. Mathewson 2002 457 11. Which resistors are in parallel? R1 R2 R4 R5 R6 R3 12. For the circuit in question #11, complete the equations V5 =____a_________ V3= ____b________ Vt = V1 +_____c_____ Vt=V4 + ___d______ I4 = _______e_______ I1 = ____f_________ It= I1 +______g_____ ( (a) V6 (b) V2 (c) V2 or V 3 (d) V5 or V 6 (e) I5 + I6 (f) I 2 + I3 (g) I 4 ) 13. If we plug in two lights in parallel the same household circuit, one 40 W and the other 120 W, then clearly the 120 W will be brighter. 120 W 120 W 40 W 120 v ac 120 v ac 40 W What happens if we mistakenly hook up the 120 W and the 40 W in series? i) the 120 W bulb is still brighter ii) the 40 W bulb is brighter iii) the bulbs are equally bright 14. If we add a resistor in parallel to a parallel circuit, what happens to the total resistance? a) it increases b) it decreases c) it may increase or decrease depending on the value of the resistance we add. Physics 12 Student Workbook ©Donald J. Mathewson 2002 458 Unit 7 Lesson 5 Exercises 1. Find R t , I t , then all voltages and currents (30. Ω 4.0 A; 1.6 A, 24V; 2.4A, 24 V; 96V,4.0A) 15 Ω 120 V 10. Ω 24 Ω 2. Find R t , I t , then all voltages and currents 15 Ω 120 V 10. Ω 15 Ω 20. Ω 10. Ω (20.Ω ,6.0A; 90.V,6.0A;30.V,2.0A;30.V,3.0A;20V,1.0A;10.V,1.0A) 3. Find the current through the 6.0Ω resistor 18 Ω 12 Ω (1.3 A) 6.0 Ω 50. V 3.0 Ω 4. Find the total resistance of the circuit (4.00Ω ) 2.00 Ω 2.00 Ω 4.00 Ω 20.0 Ω 16.0 Ω 5.00 Ω 5. Find the voltage drop across the 6.00 ohm resistor 3.00 Ω 5.00 Ω 2.00 Ω (12.6 V) 6.00 Ω 20.0 V Physics 12 Student Workbook ©Donald J. Mathewson 2002 463 6. Find the cell voltage (235 V) 20.0Ω 10.0 Ω 5.00 Ω 25.0Ω 3.00A 7. Find the cell voltage if 3.00A flows through the 6.00Ω resistor. (153 V) 2.00Ω 10.0 Ω 5.00 Ω 2.00Ω 3.00Ω 9.00Ω 6.00Ω 8. find the total current in this circuit when the switch(S) is a) open b) closed S 10.0 Ω 20.0Ω 30.0 V 5.00 Ω (2.00A; 2.14 A) 9. A 2.00 kg object is dropped from the top of a tree. Air resistance is negligible a) What is the acceleration of the falling object? (9.80m/s2) b) what is the acceleration of the Earth? (3.28×10-24 m/s 2) 10. If the surface below has µ=0.100, what is the acceleration of the system? 2.00 kg 12.0 kg 5.00 kg 40.0° Physics 12 Student Workbook ©Donald J. Mathewson 2002 (0.822 m/s2) 464 Unit 7 Lesson 6 exercises 1. Find the amount of power generated by each bulb if we connect a 40. W bulb in series with a 120. W bulb to 120. volts AC in a household circuit. (40W bulb emits 23 W; 120W bulb emits 7.5 W) 2. Find the voltage difference between the points x and y x 10. Ω 50. V 20. Ω y 5.0 Ω 15 Ω (35 V) 3. Find the voltage difference between the points x and y if 2.0 A flows though the 3.0 Ω resistors (320 V) x 20.Ω 10. Ω 3.0Ω 4.0Ω 16 Ω y 4.0Ω 2.0Ω 3.0Ω 4. Find the net voltage (Vx-Vy) for cells in series: a) cells in same 'direction' x 6 ohm 30V 10 ohm 60 V y 8 ohm b) cells opposite x 6 ohm 30V 10 ohm 60 V y 8 ohm (90V; 30V) Physics 12 Student Workbook ©Donald J. Mathewson 2002 470 5. What happens to the voltage drop across the 5Ω below when the switch is closed? Does it increase or decrease? Explain your answer. S 20Ω 10 Ω 5Ω 100 V 6. In the circuit below, the bulbs are identical. When we close the switch, what happens to the brightness of the bulbs? S A 10 V B C 7. Find the current through the 3 ohm resistor. (2 A) 2Ω 4Ω 6Ω 3Ω 6Ω 12 V Physics 12 Student Workbook ©Donald J. Mathewson 2002 471 (11.2 Ω ) 8. Find the equivalent resistance 10.0 Ω 2.0 Ω 8.00 Ω 8.00 Ω 10.0 Ω 9. Find R t and I t , then all voltages and currents (recall: equal parallel resistors split current evenly) 10 Ω 150 Ω 100 Ω 120 V 100 Ω 100 Ω (120 Ω , 1.0 A; 10.V,1.0A; 60.V,0.60A; 60.V,0.40A; 50.V,0.50A,50.V,0.50A) 10. Find the unknown voltage drops, currents, resistances 36 V I= R= 72 V V= I= R= 2A V= 4A 20V R R= 5A V= (6A 6 OHM 20V 10 OHM 5 OHM 16V 1A 16 OHM 16 V 3.2 OHM) R= 11. Find the unknown voltage drops, currents, resistances 48V 4 OHM I= 10 OHM 80V I= 200V I= R= V= Physics 12 Student Workbook ©Donald J. Mathewson 2002 V= I= R= (12A; 12A; 8A; 80V 4A 20 OHM 72V 12A 6 OHM) I= 472 12. Electrostatics review: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 Across Down 2. Two protons will_________ 1. Measured in volts per metre 5. 4 volts and 0.25 Coulomb 3. Another word for voltage 6. the charge on the electron is 4. kQ/r ________to the charge on the proton 7. kQq/r is electric ___________ 8. 2 N/C and 5 C 12. force is kQq over _________ 9. force times distance 13. kQq/r 2 10. the charge on the proton is called 18. force/field the f____________ charge 19. kQq/r 2 is known as ______'s law 11. PE = 0 at __________ 22. the units of potential 14. 2 J of work done on 1 C of charge 15. 2 protons and 2 neutrons form an _____particle 16. Joule/Coulomb 17. the force that holds the atom together 20. number of protons in the hydrogen nucleus 21. 10 N/C and 0.5 m 23. direction of the electric field (3 words) Physics 12 Student Workbook ©Donald J. Mathewson 2002 473 Unit 7 Lesson 7 Exercises and Review 1. Find the terminal voltage of a 6.0 volt cell with 0.60 Ω internal resistance that is connected to a 7.2 Ω load (5.5V) 2. Four 1.50 V cells are connected in series in the same direction inside a flashlight. If the internal resistance of each cell is 0.400 Ω and the light bulb has resistance 6.20 Ω then find the current through the bulb and the terminal voltage of each cell. (0.769 A; 1.19 V) 3. A 1.5 V dry cell is short circuited and produces a maximum current of 30. A. At this current, the terminal voltage is zero. What is the internal resistance of the cell? (0.050 Ω ) 4. A 12.0 volt cell has 8.8 V terminal voltage when it is providing 70.A of current. What is the internal resistance of the cell (0.045Ω ) 5. A 9.0 V radio cell with internal resistance 0.20 ohm is being charged. The charger is a 12 V cell with internal resistance 1.3 ohm. Find a) the terminal voltage of both cells b) the charge flow through the 9.0 V cell in 24 hrs (9.4V; 9.4V; 170 kC=1.70×105 C) 6. Write equations relating the currents and voltage drops in the circuit R2 V2 I2 Vt It R1 V1 I1 R3 V3 I3 (I t = I1 +I 2 = I1 + I3; I 2=I3; Vt =V1=V2 +V3) 7. find the total current in this circuit when the switch(S) is a) open b) closed (1.9 A; 5.2 A) S 20. V 0.50 Ω 10. Ω 5.0Ω Physics 12 Student Workbook ©Donald J. Mathewson 2002 479 8. find the total current in this circuit when the switch(S) is a) open b) closed (1.9 A; 40. A) S 10. Ω 20. V 0.50 Ω 9. Find R t and I t then all voltages and currents (50Ω ,2.0A; 20.V,2.0A; 20V,0.67A; 20.V,1.3A; 60.V,1.5A; 60.V,0.50 A ) 10. Ω 100. V 30. Ω 15 Ω 40. Ω 120 Ω 10. Find the cell voltage given that 2.00A flows through the 15.0Ω . (225V) 4.00 Ω 4.00 Ω 5.00 Ω 3.00 Ω 10.0 Ω 14.0 Ω 15.0 Ω 11. Find the unknown voltage drops and currents 2V I=3A 12 V I= 4V I= V= I= (3A; 6V 3A; 3A) 12. Find the total current on a 120. volt household circuit if we plug in a 1200. W toaster and a 60.0 Watt light bulb (10.5 A) Physics 12 Student Workbook ©Donald J. Mathewson 2002 480 13. A 5.0 kg mass slides down a rough 25° incline at constant speed. What is the net force acting on the mass? (0 N) 25° 14. A satellite orbits around the equator of the Earth with a period of 30 hours. Is it possible to move the satellite further from the Earth and keep the same orbit period? YES or NO. Explain your answer using principles of physics Earth Earth satellite T=30 hrs satellite T= 30 hrs ?? 15. In a wet climate, it is very difficult to build up a large charge with a VandeGraaf generator. Why is this? Explain using principles of physics. water vapour - O H+ H+ water molecule VdG generator 16. The cells in the circuits below are identical. Cell A has a larger terminal voltage(V t = 1.5 volts) than cell B (Vt =1.3 volts). Which of the following is true? a) cell A will last longer than cell B b) cell B will last longer than cell A c) the cells will last the same length of time A Vt=1.5 V R1 B Vt=1.3 V R2 explain your answer using principles of physics Physics 12 Student Workbook ©Donald J. Mathewson 2002 481 Lesson 8: Practice Exam Section I. Multiple Choice. (1 mark each, 25 marks total) 1. The diagram shows an electrical junction and four resistors. What is the current I 4? 2 A 4 A I=? 3 A a) 1A b) 2 A c) 3 A d) 9 A 2. An electrical toaster is rated 1500 W at 120 V. What is its resistance? a) 1500 Ω b) 13 Ω c) 19Ω d) 9.6Ω 3. The emf of a dry cell is 1.50 V. When the current through it is 6.3 × 10-2 A, the potential difference across its terminals is 1.39 V. What is the internal resistance of the cell? a) 2.4 Ω b) 22Ω c) 1.7Ω d) 46Ω **4,5 and 6******************************************* 15 Ω 60. Ω 20. Ω V A S 4. When the switch S is closed (contact), the total resistance in the circuit is: a) 7.5Ω b) 30.Ω c) 35Ω d) 55Ω 5. When the switch S is open (no contact), the reading on the ammeter is 2.0 A. When the switch is closed, the reading on the ammeter will a) increase b) not change c) decrease d) double 6. When the switch is open, the ammeter reading is 2.0 A. What is the emf of the voltage source? a) 30. V b) 60. V c) 70. V d) 110 V ***************************************************** Physics 12 Student Workbook ©Donald J. Mathewson 2002 482 7. In the circuit shown, what happens to the ammeter and voltmeter readings when the switch is closed? The ammeter reading __________ and the voltmeter reading___________. a) increases, decreases b) decreases, increases c) increases, increases d) decreases, decreases A 6V 4Ω 3Ω S 2Ω V 8. What is the current in the cell shown? a) 0.17 A b) 0.50 A c) 1.5 A d) 2.0 A 6.0 Watt 6.0 Watt 6.0 Watt 12 V 9. A certain cell has an emf of 12.0 V and an internal resistance of 0.30 Ω . If the cell is connected in a circuit where it delivers a current of 1.9 A, what is the terminal voltage? a) 0.57 V b) 11.4 V c) 12.0 V d) 12.6 V 10. If the terminal voltage of the cell in this circuit is 12.0 V and the potential difference across R 1 is 4.6 V, what is the potential difference across R 2? a) 3.7 V b) 7.4 V c) 12.0 V d) it depends on the value of R1 and R 2 R1 4.6 V R3 12.0 V R2 Physics 12 Student Workbook ©Donald J. Mathewson 2002 483 11. In this circuit, which of the following changes would cause the greatest increase in the current through the 6 Ω resistor? a) removing the 2 Ω b) removing the 4 Ω c) connecting a 2 Ω resistor between x and y d) connecting a 12 Ω resistor between x and y x 6.0 Ω 12 Ω 2.0 Ω 4.0 Ω 12.0 V y 12. If you pay 4.0 cents per kiloWatt hour, how long can you watch a 150 Watt TV if you have 6 cents? a) 7.5 hr b) 0.10 hr c) 2.5 hr d) 10. hr 13. Find the current in resistor R4. a) 0.091 A b) 0.12 A c) 0.14 A d) 0.18 A R1 3.0 V R3 33 Ω 22 Ω 12.0 V R2 R4 66 Ω 14. What is the terminal voltage of the cell. a) 10. V b) 12 V c) 4.0 V d) 6.0 V e) 16 V 3.0 Ω 2.0 Ω 10. V 15. A 50 V cell is connected to a 5.0 Ω resistor and a 10.0 Ω resistor in series. I f the current in this circuit is measured using a 0.5Ω ammeter, what reading will result? a) 3.3 A b) 3.2 A c) 0.30 A d) 2.0 A e) 15 A Physics 12 Student Workbook ©Donald J. Mathewson 2002 484 **16, 17*********************************** 10.0 Ω 2.00 Ω 20.0 Ω 16. If 60.0 W of power is dissipated in the 20.0 Ω resistor, what is the emf of the cell? a) 55.4 V b) 90.0 V c) 96.0 V d) 52.0 V e) 10.7 V 17. What is the terminal voltage of the cell? a) 58.9 V b) 53.7 V c) 94.3 V d) 52.0 V e) 92.5 V ***************************************** 18. Which picture shows an ammeter correctly reading the current through the 2 ohm resistor? a) b) 2Ω Α 2Ω 3Ω 3Ω Α c) Α d) 2Ω 2Ω 3Ω Α 19. What is R? a) 96 Ω b) 1.0× 102 Ω c) 56Ω d) 150Ω 3Ω e) 30.Ω 2.0 A 50. V 0.75 A 120 V R Physics 12 Student Workbook ©Donald J. Mathewson 2002 485 20. What is the total resistance of this circuit? a) 120Ω b) 35Ω c) 10.Ω d) 30.Ω e) 7.0 Ω 30. Ω 5.0 Ω 10. Ω V 20. Ω 21. What is the total resistance of this circuit? a) 19 Ω b) 4.6Ω c) 12Ω d) 2.7Ω e) 1.9 Ω 2.0 Ω 6.0 Ω 3.0 Ω 8.0 Ω 22. What current flows through the 3.0 Ω resistor? a) 0.84 A b) 0.75 A c) 1.1 A d) 5.3 A e) 0.86 A 2.0 Ω 3.0 Ω 10. Ω 6.0 V 2.0 Ω 23. A 3.0 Ω light bulb is connected to a 6.0 volt source. The bulb produces 11 watts of heat and light energy. What is its efficiency? a) 1.0 × 102% b) 55% c) 92% d) 61% e) 27% Physics 12 Student Workbook ©Donald J. Mathewson 2002 486 24. Consider this circuit. What current flows through the 4.0 Ω resistor and in what direction does it flow? a) 4.0 A upwards b) 2.0 A downwards c) 4.0 A downwards d) 2.0 A upwards 2.0 A 6.0 Ω 1.0 Ω 8.0 Ω 4.0 Ω V 25. For the circuit in #24, what is the cell voltage V? a) 34 V b) 58 V c) 15 V d) 44 V e) 36 V Section II. Problems (5 marks each, 25 marks total) 1. Make a graph, showing how the voltmeter reading will change as the variable resistor in the circuit is decreased. What do the slope of the graph and the y-intercept represent? variable resistor I - + V V •with less resistance,more current flows •with more current, the voltage (terminal voltage) gets smaller (Vt=e-Ir) • the equation of the line is vt = (-r) I = e •the slope is -r and so tells us the internal resistance of the cell •the y-intercept is the internal voltage of the cell (e) I Physics 12 Student Workbook ©Donald J. Mathewson 2002 487 2. Find the unknown voltage drops and currents 10 OHM V= I= V= I= 1 OHM V= I= 2 OHM 3A V= (96 V, 11A ; 90V, 9A ; 6V ; 6V, 6A ; 48 OHM V= I= 96V, 2A) 3. Find the voltage difference between the points x and y if 3.00 A flows through the 2.00 Ω resistor. Indicate steps in a clear logical order. (102 volt) x 10.0Ω 2.00Ω 5.00Ω y 3.00Ω 6.00Ω 9.00Ω 2.00Ω 4. If a current of 2.4 A runs through a light for 7.0 minutes, how many electrons have passed through the light? (6.3 × 10 21 electrons) Physics 12 Student Workbook ©Donald J. Mathewson 2002 488 5. Consider the following circuit. All of the bulbs are identical A B D 10 V S C a) rank the bulbs in order of brightness dimmest: ______ ______ ______ ______ brightest b) using principles of physics, explain your answer to a) c) what happens to the brightness of each bulb if we close the switch S? i) bulb A ii) bulb B iii) bulb C iv) bulb D (a) B=C< D < A; (b) if the current through B is I, then C will have the same current. D will have twice as much current since it has the same voltage drop as C and B together. A will have three times as much current since it has the current of bulb B/C and D ; (c) the switch S shorts out D, B and C, so they all go out. This short reduces the circuit to just bulb A. With less resistance, there is more current and so bulb A is brighter) 1 a 2 d 3 c 4 b 5 a 6 c 7 a 8 c 9 b 10 b 16 a 17 d 18 d 19 c 20 d 21 d 22 b 23 c 24 c 25 b Physics 12 Student Workbook ©Donald J. Mathewson 2002 11 c 12 d 13 a 14 c 15 b 489