S15--Physics current and Circuit PRACTICE

Transcription

1 Name: Class: Date: ID: A S5--Physics current and Circuit PRACTICE Multiple Choice Identify the choice that best completes the statement or answers the question.. Three resistors, with values of 2.0, 4.0 and 8.0 Ω, respectively, are connected in parallel. What is the overall resistance of this combination? a. 4.0 Ω b Ω c. 7.0 Ω d Ω e.. Ω 2. A hair dryer draws 200 W, a curling iron draws 800 W, and an electric light fixture draws 500 W. If all three of these appliances are operating in parallel on a 20-V circuit, what is the total current drawn? a A b A c. 9.4 A d A e A 3. If a 500-W heater carries a current of 4.00 A, what is the resistance of the heating element? a. 3.3 Ω b..2 Ω c. 0.0 Ω d Ω e Ω 4. Three resistors connected in parallel have the individual voltages labeled V, V 2 and V 3, respectively. Which of the following expresses the total voltage V T across the three resistors when connected in this manner? a. V T V + V 2 + V 3 b. V T 3 V 3 V 2 3 V 3 c. V T V V 2 V 3 d. V T (/ V + / V 2 + / V 3 ) e. V T (/ V + / V 2 + / V 3 ) 5. You measure a 25.0-V potential difference across a 5.00-Ω resistor. What is the current flowing through it? a A b. 25 A c A d A e..00 A 6. If ε 20 V, at what rate is thermal energy being generated in the 20-Ω resistor? a. 3.4 W b. 6.5 W c. 5 W d..6 W e. 26 W 7. An electric car is designed to run off a bank of 2-V batteries with total energy storage of J. If the electric motor draws W, what current will be delivered to the motor? a. 00 A b. 200 A c. 50 A d. 500 A e. 400 A 8. Three resistors, each with resistance R, are in series in a circuit. They are replaced by one equivalent resistor, R. Comparing this resistor to the first resistor of the initial circuit, which of the following is true? a. The voltage across uals the voltage across R. b. R is less than R. c. The power given off by uals the power given off by R. d. R is equal to R. e. The current through uals the current through R. 9. What is Kirchhoff's st equation for this junction? a. I 2 I 3 b. I 2 I + I 3 c. I 3 I + I 2 d. I + I 2 + I 3 0 e. I I 2 + I 3 0. When an electric current exists within a conducting wire, which of the following statements describes the condition of any accompanying electric field? a. must be parallel to current flow b. must be zero c. must be perpendicular to current flow d. must be anti-parallel (opposite direction) to current flow e. None of the above choices is valid.

2 Name: ID: A. An electric toaster requires 00 W at 0 V. What is the resistance of the heating coil? a. 7.5 Ω b. 9.0 Ω c. 3.0 Ω d. 0.0 Ω e..0 Ω 2. A superconducting wire's chief characteristic is which of the following? a. a large cross sectional area b. an extremely high temperature c. no resistance d. an extremely great length e. a great number of charge carriers 3. How is current affected if the time interval over which the charge passes through a given area decreases while the amount of charge remains the same? a. The current is not affected. b. The current initially increases and then is gradually restored. c. The current increases. d. The current decreases. 4. If ε 9.0 V, what is the current in the 5-Ω resistor? a A b. 0.5 A c A d. 0 0 A e A 5. An 8.00-Ω resistor is dissipating 00 watts. What are the current through it, and the difference of potential across it? a A, 2.5 V b. 2.5 A, 3.54 V c. 2.5 A, 28.3 V d A, 28.3 V e A, 3.54 V 6. A light bulb has resistance of 240 Ω when operating at 20 V. Find the current in the light bulb. a. 2.0 A b A c A d A e..0 A 7. The two ends of a 3.0-Ω resistor are connected to a 9.0-V battery. What is the current through the resistor? a. 0.7 A b. 27 A c. 3.0 A d. 6.3 A e A 8. The current in an electron beam in a cathode-ray tube is A. How much charge hits the screen in 5.0 s? a C b C c C d C 9. How much power is being dissipated by one of the 0-Ω resistors? a. 9.6 W b. 6.4 W c. 8.2 W d. 6 W e. 24 W 20. Two positive point charges are initially separated by a distance of 2 cm. If their separation is increased to 6 cm, the resultant electrical potential energy is equal to what factor multiplied by the initial electrical potential energy? a. 9 b. 3 c. 3 d If ε 24 V, at what rate is thermal energy generated in the 20-Ω resistor? a. 0.5 W b. 3 W c. 39 W d. 3.2 W e. 23 W 2

3 Name: ID: A 22. If electrical energy costs 5.5 cents per kwh, what does it cost to heat 200 kg water from 5 C to 80 C? (The specific heat of water 0 3 cal/kg C and.0 cal 4.86 J.) a. 83 cents b. 48 cents c. 80 cents d. 25 cents e. 6 cents 23. If R < < R 3, and if these resistors are connected in series in a circuit, which one dissipates the greatest power? a. More information is needed. b. All are equal in power dissipation. c. R d. e. R A light bulb, sold as long-lasting, is rated 00 W at 30 V. The "increased" lifetime comes from using it at 20 V. Assuming negligible change in resistance at the different voltage, what is its power consumption at 20 V? a. 08 W b. 92 W c. 00 W d. 32 W e. 85 W 25. How is current affected if the number of charge carriers decreases? a. The current increases. b. The current decreases. c. The current initially decreases and then is gradually restored. d. The current is not affected. 26. A 500-W heater carries a current of 4.0 A. How much does it cost to operate the heater for 30 min if electrical energy costs 6.0 cents per kwh? a. 8 cents b. 95 cents c..5 cents d. 9.0 cents e. 36 cents 27. A 60-W light bulb is in a socket supplied with 20 V. What is the current in the bulb? a A b. 60 A c. 2.0 A d A e A 28. The unit of electric resistance, the ohm, is equivalent to which of the following? a. A/s b. A/V c. V/A d. A/m e. V m 29. An electric car is designed to run off a bank of 2-V batteries with total energy storage of J. If the electric motor draws W in moving the car at a steady speed of 0 m/s, how far will the car go before it is "out of juice?" a. 25 km b. 50 km c. 50 km d. 250 km e. 00 km 30. The current in an electron beam in a cathode-ray tube is measured to be 70 µa. How many electrons hit the screen in 5.0 s? (e C) a electrons b electrons c electrons d electrons e electrons 3. Which two resistors are in parallel with each other? a. R and R4 b. R and R c. R and R2 d. R2 and R3 e. R2 and R4 32. Three resistors with values of R, and R 3, respectively, are connected in series. Which of the following expresses the total resistance, R T, of the three resistors? a. R T (/R + / + /R 3 ) b. R T R R 3 c. R T R + + R 3 d. R T 3R 3 3R 3 e. R T (/R + / + /R 3 ) 33. Three 8.0-Ω resistors are connected in parallel. What is their equivalent resistance? a Ω b. 4.5 Ω c. 0.3 Ω d. 2.7 Ω e Ω 34. An electric clothes dryer draws 5 A at 220 V. If the clothes put into the dryer have a mass of 7.0 kg when wet and 4.0 kg dry, how long does it take to dry the clothes? (Assume all heat energy goes into vaporizing water, L v J/kg.) a. 20 min b. 34 min c. 6 min d. min e. 55 min 35. Three resistors connected in parallel each carry currents labeled I, I 2 and I 3. Which of the following expresses the value of the total current I T in the combined system? a. I T I I 2 I 3 b. I T I + I 2 + I 3 c. I T 3I 3I 2 3I 3 d. I T (/I + /I 2 + /I 3 ) e. I T (/I + /I 2 + /I 3 ) 36. When a positive charge moves in the direction of the electric field, what happens to the electrical potential energy associated with the charge? a. It remains the same. b. It increases. c. It sharply increases, and then decreases. d. It decreases. 3

4 Name: ID: A 37. Household 20-V outlets are made to accept three-pronged plugs. One of the prongs attaches to the "live" wire at 20 V, and another attaches to the "neutral" wire that is connected to ground. What is the round third prong for? a. It connects the case of the appliance directly to ground for safety purposes. b. It lets the appliance run if the neutral wire breaks. c. Nothing electrical, it is for mechanical sturdiness. d. It serves for direct current feed. e. It serves as a backup to the hot wire. 38. A high-voltage transmission line carries 000 A at 700 kv for a distance of 00 miles. If the resistance in the wire is Ω/mile, what is the power loss due to resistive losses? a. 0 GW b. 00 MW c. 0 MW d. 0 kw e. 00 kw 39. Three resistors connected in parallel have individual values of 4.0, 6.0 and 0.0 Ω, respectively. If this combination is connected in series with a 2-V battery and a 2.0-Ω resistor, what is the current in the 0-Ω resistor? a A b. 23 A c..0 A d. A e. 6 A 40. Four.5-volt AA batteries in series power a transistor radio. If the batteries hold a total charge of 240 C, how long will they last if the radio has a resistance of 200 Ω? a. 5 h b. 4. h c. 2.2 h d. 3 h e.. h 4. In a circuit, a current of 2.0 A is drawn from a battery. The current then divides and passes through two resistors in parallel. One of the resistors has a value of 64 Ω and the current through it is 0.40 A. What is the value of the other resistor? a. 24 Ω b. 8.0 Ω c. 32 Ω d. 40 Ω e. 6 Ω 42. The following three appliances are connected to a 20-V house circuit: i) toaster, 200 W, ii) coffee pot, 750 W, and iii) microwave, 800 W. If all were operated at the same time, what total current would they draw? a. 3 A b. 23 A c. 0 A d. 5.0 A e. 3.0 A 43. If a 500-W heater carries a current of 4.00 A, what is the voltage across the ends of the heating element? a V b V c. 25 V d. 250 V e V 44. A resistor is connected to a battery with negligible internal resistance. If you replace the resistor with one that has twice the resistance, by what factor does the power dissipated in the circuit change? a b. 4.0 c d. 2.0 e Three resistors with values R, and R 3, respectively, are connected in parallel. Which of the following expresses the total resistance, R T, of the three resistors when connected in parallel? a. R T (/R + / + /R 3 ) b. R T (/R + / + /R 3 ) c. R T R + + R 3 d. R T R R 3 e. R T 3R 3 3R Three resistors, each with resistance R, are in parallel in a circuit. They are replaced by one equivalent resistor, R. Compare this resistor to the first resistor of the initial circuit. Which of the following statements is true? a. The voltage across uals the voltage across R. b. R is less than R. c. R is greater than R. d. The current through uals the current through R. e. The power given off by uals the power given off by R. 47. The internal resistances of an ideal voltmeter and an ideal ammeter are respectively (ideal meaning the behavior of the system is not changed when using the meter): a. Both resistances are finite and non-zero. b. infinite and zero. c. infinite and infinite. d. zero and infinite. e. zero and zero. Problem 48. Three resistors with values of 2 Ω, 38 Ω, 25 Ω, respectively, are connected in series. What is their equivalent resistance? 49. A current of 0.20 A passes through a 3.0 Ω resistor. The resistor is connected in series with a 6.0 V battery and an unknown resistor. What is the resistance value of the unknown resistor? 50. Three resistors with values of 6 Ω, 9 Ω, 26 Ω, respectively, are connected in parallel. What is their equivalent resistance? 4

5 Name: ID: A 5. Three resistors with values of 8 Ω, 26 Ω, 9 Ω, respectively, are connected in series. What is their equivalent resistance? 52. Three resistors with values of 28 Ω, 58 Ω, 22 Ω, respectively, are connected in series. What is their equivalent resistance? 53. In the circuit shown above, the current in the 3.9 Ω resistor is 0.27 A. What is the voltage of the battery? 54. What is the current through the 8.20 Ω resistor in the circuit shown above? 55. What is the current in the 8 Ω resistor in the circuit shown in the figure above? 56. What is the current in the 2 Ω resistor in the circuit shown in the figure above? 57. Two resistors having values of 4.9 Ω and 9. Ω are wired in parallel. This pair of resistors is wired in series with a second pair of parallel resistors having values of 3.6 Ω and 8.6 Ω. If the current in the 9. Ω resistor is 0.25 A, what is the voltage across the entire circuit? 58. Four resistors are wired in parallel with a 2.50 V battery. The total circuit current is.85 A, and three of the resistors have resistances of 2.70 Ω, 8.20 Ω, and 2.6 Ω. What is the resistance of the fourth resistor? 59. Three resistors with values of 5 Ω, 4 Ω, 58 Ω, respectively, are connected in parallel. What is their equivalent resistance? 60. Three resistors with values of 27 Ω, 8 Ω, 6 Ω, respectively, are connected in parallel. What is their equivalent resistance? 5

6 S5--Physics current and Circuit PRACTICE Answer Section MULTIPLE CHOICE. ANS: E PTS: DIF: 2 TOP: 8. Sources of emf 8.2 Resistors in Series 8.3 Resistors in Parallel 2. ANS: A PTS: DIF: 2 TOP: 8.6 Household Circuits 8.7 Electrical Safety 3. ANS: A PTS: DIF: 2 TOP: 7.8 Electrical Energy and Power 4. ANS: C PTS: DIF: TOP: 8. Sources of emf 8.2 Resistors in Series 8.3 Resistors in Parallel 5. ANS: A PTS: DIF: TOP: 7.4 Resistance and Ohm's Law 6. ANS: D PTS: DIF: 3 TOP: 8. Sources of emf 8.2 Resistors in Series 8.3 Resistors in Parallel 7. ANS: D PTS: DIF: 2 TOP: 7.8 Electrical Energy and Power 8. ANS: E PTS: DIF: TOP: 8. Sources of emf 8.2 Resistors in Series 8.3 Resistors in Parallel 9. ANS: D PTS: DIF: TOP: 8.4 Kirchhoff's Rules and Complex DC Circuits 0. ANS: A PTS: DIF: TOP: 7.2 A Microscopic View: Current and Drift Speed. ANS: E PTS: DIF: 2 TOP: 7.8 Electrical Energy and Power 2. ANS: C PTS: DIF: TOP: 7.7. Superconductors 3. ANS: C PTS: DIF: II 4. ANS: A PTS: DIF: 2 TOP: 8. Sources of emf 8.2 Resistors in Series 8.3 Resistors in Parallel 5. ANS: D PTS: DIF: 2 TOP: 7.8 Electrical Energy and Power 6. ANS: B PTS: DIF: TOP: 7.8 Electrical Energy and Power 7. ANS: C PTS: DIF: TOP: 8. Sources of emf 8.2 Resistors in Series 8.3 Resistors in Parallel 8. ANS: A I A t 5.0 s I Q t Rearrange to solve for Q. Q I t ( A)(5.0 s) C PTS: DIF: IIIA 9. ANS: B PTS: DIF: 2 TOP: 8. Sources of emf 8.2 Resistors in Series 8.3 Resistors in Parallel 20. ANS: B PTS: DIF: II 2. ANS: B PTS: DIF: 3 TOP: 8. Sources of emf 8.2 Resistors in Series 8.3 Resistors in Parallel 22. ANS: A PTS: DIF: 3 TOP: 7.8 Electrical Energy and Power 23. ANS: E PTS: DIF: 2 TOP: 8. Sources of emf 8.2 Resistors in Series 8.3 Resistors in Parallel 24. ANS: E PTS: DIF: 2 TOP: 7.8 Electrical Energy and Power 25. ANS: B PTS: DIF: II 26. ANS: C PTS: DIF: 2 TOP: 7.8 Electrical Energy and Power 27. ANS: A PTS: DIF: TOP: 7.8 Electrical Energy and Power

7 28. ANS: C PTS: DIF: TOP: 7.4 Resistance and Ohm's Law 29. ANS: C PTS: DIF: 2 TOP: 7.8 Electrical Energy and Power 30. ANS: A PTS: DIF: TOP: 7. Electric Current 3. ANS: D PTS: DIF: 2 TOP: 8. Sources of emf 8.2 Resistors in Series 8.3 Resistors in Parallel 32. ANS: C PTS: DIF: TOP: 8. Sources of emf 8.2 Resistors in Series 8.3 Resistors in Parallel 33. ANS: D PTS: DIF: 2 TOP: 8. Sources of emf 8.2 Resistors in Series 8.3 Resistors in Parallel 34. ANS: B PTS: DIF: 3 TOP: 7.8 Electrical Energy and Power 35. ANS: B PTS: DIF: TOP: 8. Sources of emf 8.2 Resistors in Series 8.3 Resistors in Parallel 36. ANS: D PTS: DIF: I 37. ANS: A PTS: DIF: TOP: 8.6 Household Circuits 8.7 Electrical Safety 38. ANS: B PTS: DIF: 2 TOP: 7.8 Electrical Energy and Power 39. ANS: A PTS: DIF: 3 TOP: 8. Sources of emf 8.2 Resistors in Series 8.3 Resistors in Parallel 40. ANS: C PTS: DIF: 2 TOP: 8.4 Kirchhoff's Rules and Complex DC Circuits 4. ANS: E PTS: DIF: 2 TOP: 8.4 Kirchhoff's Rules and Complex DC Circuits 42. ANS: B PTS: DIF: 2 TOP: 8.6 Household Circuits 8.7 Electrical Safety 43. ANS: C PTS: DIF: TOP: 7.8 Electrical Energy and Power 44. ANS: A PTS: DIF: 2 TOP: 7.8 Electrical Energy and Power 45. ANS: B PTS: DIF: TOP: 8. Sources of emf 8.2 Resistors in Series 8.3 Resistors in Parallel 46. ANS: A PTS: DIF: TOP: 8. Sources of emf 8.2 Resistors in Series 8.3 Resistors in Parallel 47. ANS: B PTS: DIF: 2 TOP: 8. Sources of emf 8.2 Resistors in Series 8.3 Resistors in Parallel PROBLEM 48. ANS: 75 Ω R 2 Ω 38 Ω R 3 25 Ω R + + R 3 2 Ω + 38 Ω + 25 Ω 75 Ω PTS: DIF: I 2

8 49. ANS: 27 Ω I R 0.20 A R 3.0 Ω V batt 6.0 V V R R I l 3.0 Ω 0.20 A 0.60 V V R2 V batt V R 6.0 V 0.60 V 5.4 V I R2 I R 0.20 A V R2 5.4 V I R A 27 Ω PTS: DIF: IIIB 50. ANS: 6.5 Ω R 6 Ω 9 Ω R 3 26 Ω R + + R 3 6 Ω + 9 Ω + 26 Ω Ω Ω Ω 0.53 Ω Ω Ω PTS: DIF: IIIA 5. ANS: 53 Ω R 8 Ω 26 Ω R 3 9 Ω R + + R 3 8 Ω + 26 Ω + 9 Ω 53 Ω PTS: DIF: I 3

9 52. ANS: 08 Ω R 28 Ω 58 Ω R 3 22 Ω R + + R 3 28 Ω + 58 Ω + 22 Ω 08 Ω PTS: DIF: I 53. ANS: 2.3 V R 4.2 Ω 9. Ω R Ω R Ω R Ω I R A R,2 R Ω + 9. Ω 0.24 Ω + 0. Ω 0.35 Ω R,2 Ω Ω + R 4,5 R 4 R Ω Ω 0.45 Ω Ω 0.58 Ω R 4,5 Ω Ω R,2 + R 3 + R 4,5 2.9 Ω Ω +.7 Ω 8.5 Ω I ckt I R3 V batt ( )(I ckt ) (8.5 Ω)(0.27 A) 2.3 V PTS: DIF: IIIC 4

10 54. ANS: A V 7.50 V R 5.5 Ω 3.85 Ω R Ω R Ω R Ω Find for R 4 and R 5 : + R 4,5 R 4 R Ω Ω 0.22 Ω Ω 0.58 Ω R 4,5 Ω Ω R is not used for the calculations as it is simply in parallel with the remainder of the circuit. Find the equivalent resistance for the part of the circuit that includes R 4 : + R 3 + R 4, Ω Ω Ω 8.3 Ω Find the current through this resistance: I ckt V 7.50 V 8.3 Ω 0.44 A Use this current to find the voltage across R 4,5 : V R4,5 (I ckt )(R 4,5 ) (0.44 A)(6.33 Ω) 2.62 V Find the current through R 4 : I R4 V R4,5 R V 8.20 Ω A PTS: DIF: IIIC 55. ANS: A R 2 Ω 8 Ω V 8 V V 2 6 V Because one side of is connected to the 6 V battery and the other side is connected to the 8 V battery, the voltage across must be the difference between the battery voltages. V R2 V 2 V 6 V 8 V 8 V I R2 V R2 8 V 8 Ω A PTS: DIF: IIIB 5

11 56. ANS: 4 A R 2 Ω 8 Ω V 8 V V 2 6 V The voltage across R must be equal to 8 V, because R is connected directly across the 8 V battery. I R V R 8 V 2 Ω 4 A PTS: DIF: IIIB 57. ANS: 4. V R 4.9 Ω 9. Ω R Ω R Ω I R A V R2 (I R2 )( ) (0.25 A)(9. Ω) 2.3 V I R V R2 2.3 V 4.9 Ω 0.47 A I ckt I R2 + I R 0.25 A A 0.72 A + R 3,4 R 3 R 4 R 3,4 Ω Ω 3.6 Ω Ω 0.28 Ω Ω 0.40 Ω V R3,4 (I ckt )(R 3,4 ) (0.72 A)(2.5 Ω).8 V V ckt V R2 + V R3,4 2.3 V +.8 V 4. V PTS: DIF: IIIC 6

12 58. ANS: 5.94 Ω V batt 2.50 V I total.85 A R 2.70 Ω 8.20 Ω R Ω I R V batt R 2.50 V 2.70 Ω A I R2 V batt 2.50 V 8.20 Ω A I R3 V batt R V 2.6 Ω 0.98 A I R4 I total (I R + I R2 + I R3 ).85 A (0.926 A A A) I R4.85 A.429 A 0.42 A V batt R V I R A 5.94 Ω PTS: DIF: IIIB 59. ANS: 9.3 Ω R 5 Ω 4 Ω R 3 58 Ω R + + R 3 5 Ω + 4 Ω + 58 Ω Ω Ω Ω 0.08 Ω Ω Ω PTS: DIF: IIIA 7

13 60. ANS: 9.0 Ω R 27 Ω 8 Ω R 3 6 Ω R + + R 3 27 Ω + 8 Ω + 6 Ω Ω Ω Ω 0. Ω Ω Ω PTS: DIF: IIIA 8