UIT E UMMARY KEY COCEPT CHAPTER UMMARY 11 The principles of conservation of energy and charge apply to electrical circuits. Electrical circuits Conventional current and electron flow Current, electrical potential difference, and resistance Kirchhoff s voltage law eries, parallel, and mixed circuits Kirchhoff s current law Power and power consumption An electrical circuit contains an energy source, conductors, and a load. (11.1) Ohm s law describes the relationship between current, potential difference, and resistance in a circuit. (11.1) Kirchhoff s voltage law states that in any closed circuit loop, the sum of the potential differences through all the components must be zero. (11.2) In a series circuit, the current is constant, the total resistance is the sum of the resistors, and the total voltage of the battery equals the sum of the voltage drops across the resistors. (11.2) Kirchhoff s current law states that the current entering a junction must be equal to the current leaving the junction. (11.3) In a parallel circuit, the total current equals the sum of the currents through each branch, the total resistance decreases as the number of branches increases, and the voltage is constant across each branch. (11.3) Power is the rate at which electrical energy is transferred. (11.4) The power consumed by an electrical appliance can be determined. (11.4) 12 Properties of magnetic fields apply in nature and technology. Characteristics and properties of magnetic fields Oersted s principle The motor principle The law of magnetism states that like magnetic poles repel each other and unlike poles attract each other. (12.1) A magnetic field is the three-dimensional region around a magnet in which magnetic forces are exerted. (12.1) Oersted s principle states that when a current moves through a conductor, it creates a magnetic field. (12.1) The motor principle states that a current-carrying conductor will experience a magnetic force as long as the conductor is not parallel to the magnetic field. (12.2) The factors that affect the strength of the magnetic force are the current, the magnetic field, and the length and orientation of the conducting wire. (12.2) The electric motor, loudspeaker, and particle accelerator all operate according to the motor principle. (12.3) 13 Electromagnetic induction is used to generate most of the electrical energy used today. Faraday s law of induction Lenz s law Operation of a generator Generation of electrical energy tep-up and step-down transformers The law of electromagnetic induction states that a changing magnetic field in the region of a conductor can induce an electric current in a closed loop. (13.1) Faraday s law of electromagnetic induction states that a changing magnetic field in the region of a closed-loop conductor will induce an electric current. (13.1) Lenz s law states that an induced current and emf are in such a direction as to oppose the change that produced them. (13.1) A generator converts mechanical energy to electrical energy. (13.2) Methods of generating electrical energy involve using flowing water, burning fuels, or using nuclear, wind, tidal, solar, or geothermal energy. (13.2) Each method of generating electricity has an environmental impact. (13.2) A transformer can step up (increase) or step down (decrease) voltage. (13.3) There are precautions related to keeping the public safe from the hazards of high voltage. (13.3) 442 Unit E ummary
UIT E REVIEW ACHIEVEMET CHART CATEGORIE k Knowledge and understanding t Thinking and investigation c Communication a Application Key Terms Review 1. Create a concept map that links all of the terms in the list below. Give examples, where applicable, of the various terms. k battery conventional current electron flow direct current (DC) alternating current (AC) resistance potential difference (voltage) Ohm s law series circuit Kirchhoff s voltage law parallel circuit Kirchhoff s current law power magnetic field magnetic force Oersted s principle motor principle electromagnetic induction Faraday s law of electromagnetic induction Lenz s law generator step-up transformer step-down transformer Key Concept Review CHAPTER 11 2. Draw a circuit diagram of a series circuit showing three light bulbs, a battery, a switch, a voltmeter, and an ammeter. k 3. (a) How does conventional current differ from electron flow? k (b) How does the direction of current flow affect circuit analysis? k 4. Determine the current produced by a battery that delivers 450.0 C in 25.0 min. t 5. Explain how Ohm s law relates current, potential difference, and resistance. k 6. Copy the following circuit diagram into your notes and add a voltmeter and ammeter in the proper location to measure the total current and the voltage drop across resistor 2. k Question 6 7. In the following diagram, identify where the electrical potential is zero. t Question 7 8. Explain how Kirchhoff s current and voltage laws are used in the analysis of series and parallel circuits. k 9. Draw a series circuit that has four resistors of 10, 20, 30, and 40 Ω connected to a 6.0-V battery. (a) Determine the total resistance and current. t (b) Find the voltage drop through the 30-Ω resistor. t 10. What is power and how is power consumption determined? k CHAPTER 12 R 1 A C F E D R 2 11. What is a magnetic field? k 12. Explain why magnetic field lines cannot cross each other, even if they originate from separate magnets. k 13. Draw two uniform magnetic fields where one is stronger than the other. Label each field. k 14. Explain the effect that a magnetic field has on a current-carrying conductor when there is no current. t 15. (a) Explain Oersted s principle. k (b) What effect did Oersted s observations have on the study of electricity? k Unit E Review 443
16. (a) Give two characteristics of the magnetic field created by a straight current-carrying conductor. k (b) Give two characteristics of a magnetic field created by a solenoid. k 17. Describe the three factors that influence the strength of a magnetic field in an electromagnet. k 18. (a) Explain, in your own words, the motor principle. k (b) Identify and explain the factors that influence the motor principle. k CHAPTER 13 19. (a) Explain Faraday s law of induction in your own words. k (b) What is the significance of Faraday s law? k 20. (a) Explain Lenz s law in your own words. c (b) How does Lenz s law work with Faraday s law? k 21. Explain the role of a generator in the production of electricity. k 22. Why are transformers used in the transmission of electricity? k 23. Explain the difference between a step-up transformer and a step-down transformer. k Connect Your Understanding 24. A charge of 68.0 C experiences a change in potential energy of 5.0 10 2 J as it flows through an electric relay. What is the electrical potential difference of the relay? t 25. Determine the value of R 2 in the following circuit. t 27. (a) Redraw the following circuit to make an equivalent series circuit with two resistors: R 3 and R //. a (b) A current of 50.0 ma flows through the ammeter. What is the potential difference of the battery? t (c) Determine the voltage drop through all the resistors. t (d) Determine the current through R 1 and R 2. t (e) Determine the power dissipated by each resistor. t V T Question 27 28. Determine the voltage drop and the power dissipated by each resistor in the following diagram. t Question 28 29. Explain why two magnets in the same orientation stored in a cabinet side-by-side would both weaken over time. t 30. ketch the magnetic fields that would result from the following magnet orientations. t R 3 2.0 k R 1 6.0 R 2 3.0 R 3 4.0 R 1 5.0 k R 2 20.0 k I 10.0 A R 1 5.0 V T 48.0 V Question 25 26. Determine the current through R 3 in the following circuit. t V T 200.0 V Question 26 I 3.0 A R 1 5.0 R 3 8.0 R 2 15.0 R 2? R 3 25.0 Question 30 31. A bent rigid wire rests on a table in an external magnetic field that runs left to right. A 0.260 A current moves through the wire as shown in the diagram on the next page. (a) Wire segments A and CD are both 30.0 cm long. Determine the magnetic force on segments A and CD. t (b) Determine the magnetic force on segment C. t (c) If the mass of segment ACD is 5.00 g, will the wire lift off the table? t 444 Unit E Review
25.0 cm C A D I 0.8007 T 36. A wire is wound into three square loops and positioned in an external magnetic field as shown below. If the length of one side of a loop is 15.0 cm and the wire carries a current of 8.00 A, determine the strength of the magnetic field that would produce a force of 1.50 to the right. t Question 31 32. Wire segment A is 6.00 cm long and perpendicular to the 0.380-T external magnetic field of a horseshoe magnet as shown below. A experiences a force of 1.14 10 2 [down]. Determine the magnitude and direction of the current in the wire. t A Question 32 33. A wire carrying a direct current of 15.0 A [east] runs between two telephone poles positioned 30.0 m apart. The telephone wire is perpendicular to Earth s magnetic field of 5.0 10 5 T [north]. Determine the force on the wire between the two poles. t 34. A force of 60.0 [up] is exerted on a wire carrying a current of 37.6 A [south] by a magnetic field of 2.90 T [east]. Determine the length of the wire perpendicular to the field. t 35. A metal plate is sliding along a table in the direction of the velocity vector shown below. An external magnetic field of 5.00 T runs vertically upward through the metal plate. Two insulated wires are attached as shown in the diagram. Determine the current reading in both ammeters. t Question 36 37. Explain why a two-pole brushed DC motor is an improvement over a single loop DC motor. t 38. Why is a three-pole DC motor superior in design to a two-pole motor? t 39. Identify and explain one disadvantage that all brushed DC motors have. t 40. List three devices (not described in the text) that use an electric motor. t 41. Explain, using your own words, how a magnetic speaker cone is made to vibrate back and forth to produce a sound. c 42. A stream of moving charged particles can experience a force if they move through an external magnetic field. Explain how this is an example of the motor principle. t 43. If a current is induced in a wire as it moves perpendicularly through a magnetic field, explain why the motor principle is also a natural consequence. t 44. The following diagram shows a wire that has a velocity to the right. Indicate the direction of the induced current. t A v v Question 44 Question 35 Unit E Review 445
45. The following diagram shows a wire in an external magnetic field with an induced current. (a) Indicate the direction of the resulting force on the wire. t (b) If the current is induced because of the motion in the diagram shown in question 44, what can we say about the velocity and resulting force on the wire? t Data for Question 48 Potential Difference (V) 0.00 0.00 6.50 0.20 13.3 0.40 19.7 0.60 Current (A) 26.3 0.80 Question 45 46. A current of 4.00 A flows through the secondary coil of a 240-W transformer to a 380.0-Ω resistor. There are 280 turns in the primary coil and 30 turns in the secondary coil. (a) Determine the voltage in the secondary circuit. t (b) Determine the voltage in the primary circuit. t kills Practice I 47. Redraw the following circuit diagram in your notebook. (a) Where would you position a voltmeter to determine the voltage drop across R 1? a (b) What is the value of R 1? t 49. During an experiment, a student wires two light bulbs together as shown below. (a) Describe the type of wiring that this design represents. a (b) Draw the circuit diagram for this circuit. a (c) A classmate believes that there should be a wire from terminal A to terminal. Draw the circuit diagram for this arrangement, and describe what changes it would make to the voltage and current through light bulb 1. a Question 49 50. Explain or sketch the type of motor that could have produced the following graph. t F rot 1 2 A C D Rotational Force vs. Armature Angle V T 144 V Question 47 R 1? I 1.50 A R 2 48.0 48. Plot a potential difference vs. current graph from the data given in the following table. Use the graph to determine the resistance of the circuit. a R 3 0 90 180 270 360 72.0 Armature Angle Question 50 51. Use the right-hand rule to determine the direction of motion of the magnet relative to the solenoid if the current moves through the solenoid as shown. a Question 51 446 Unit E Review
52. A magnet is dropped through a non-magnetic copper tube as shown below. Explain what effect, if any, you would expect to see as the magnet falls. t 53. Give three different right-hand rules that were explained in this unit. Draw diagrams of the conductor, magnetic field, and force (if applicable) that are associated with each rule. t Revisit the ig Ideas and Fundamental Concepts 54. Explain how an understanding of the relationship between electricity and magnetism was built on various scientists observations and experiments. t 55. Explain how the properties of magnetic fields and the flow of current make it possible to produce and transmit electricity. t cience, Technology, ociety, and the Environment 56. Explain why power transmission from a power plant to distant cities requires the use of a transmission substation and distribution v Question 52 substations. In your explanation, be sure to discuss why the voltage during transmission must be very high mandating the use of alternating current instead of direct current. c 57. Copy the following table in your notebook and complete the information for the different electricity generation technologies discussed in the text. t Electricity Generating Methods Method of Generating Electricity 58. Make a list of all the technologies that you use that do not rely on the concepts of electromagnetism. What does this tell you about electromagnetism? c Reflection Is an Electric Generator Used? Advantages and Disadvantages 59. Identify the topic in this unit that you found the most interesting. Explain why. c 60. What could you do to improve the quality of your work in the activity and investigations you did in this unit? Consider the way you work in groups, as well as your individual work. c E17 Unit Task PHYIC OURCE Rev It Up! Question How can you design and build a DC motor? Figure 13.35 A cross-section of a motor Task Overview DC motors have revolutionized the way we live. An electric motor does not create any pollution and can operate for years without maintenance. In this task, you will use the concepts that you learned in this unit to design and build a DC motor. The purpose of your motor will be to lift as much weight as possible from the floor to a desk using 9.0 V. You will only be allowed to use materials found in a local hardware store. You will need to know how to wire series and parallel circuits, to understand the motor principle, and to understand how a simple DC motor is designed. Remember to completely design your motor before you begin building. Your teacher will provide you with a complete task description. Unit E Review 447