13 Physics 11se Ue End

7/27/2019 13 Physics 11se Ue End

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SUMMARY

442 Unit E Summary

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EKEY CONCEPTS CHAPTER SUMMARY

The principles of conservation of energy and charge apply to electrical circuits. Electrical circuits Conventional current and

electron flow Current, electrical

potential difference, andresistance

Kirchhoffs voltage law Series, parallel, and

mixed circuits Kirchhoffs current law Power and power

consumption

An electrical circuit contains an energy source, conductors, and a load. (11.1) Ohms law describes the relationship between current, potential difference, and resistance in a circuit.

(11.1) Kirchhoffs 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) Kirchhoffs 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 eachbranch. (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)

Properties of magnetic fields apply in nature and technology.

Characteristics andproperties of magneticfields

Oersteds principle The motor principle

The law of magnetism states that like magnetic poles repel each other and unlike poles attract eachother. (12.1)

A magnetic field is the three-dimensional region around a magnet in which magnetic forces areexerted. (12.1)

Oersteds 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 asthe 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 thelength and orientation of the conducting wire. (12.2)

The electric motor, loudspeaker, and particle accelerator all operate according to the motor principle. (12.3)

Electromagnetic induction is used to generate most of the electrical energy used today.

Faradays law of induction Lenzs law Operation of a generator Generation of electrical

energy Step-up and step-down

transformers

The law of electromagnetic induction states that a changing magnetic field in the region of a conductorcan induce an electric current in a closed loop. (13.1)

Faradays law of electromagnetic induction states that a changing magnetic field in the region of aclosed-loop conductor will induce an electric current. (13.1)

Lenzs law states that an induced current and emf are in such a direction as to oppose the changethat 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)

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REVI EW

Unit E Review 443

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Key Terms Review1. Create a concept map that links all of the

terms in the list below. Give examples, whereapplicable, of the various terms. k

battery conventional current electron flow direct current (DC) alternating current (AC) resistance potential difference (voltage) Ohms law series circuit

Kirchhoffs voltage law parallel circuit Kirchhoffs current law power magnetic field magnetic force Oersteds principle motor principle electromagnetic induction Faradays law of electromagnetic induction Lenzs law generator step-up transformer step-down transformer

Key Concept Review

CHAPTER 112. 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 batterythat delivers 450.0 C in 25.0 min. t

5. Explain how Ohms law relates current,potential difference, and resistance. k

6. Copy the following circuit diagram into yournotes and add a voltmeter and ammeter in theproper location to measure the total currentand the voltage drop across resistor 2. k

Question 6

7. In the following diagram, identify where theelectrical potential is zero. t

Question 7

8. Explain how Kirchhoffs current and voltagelaws are used in the analysis of series andparallel circuits. k

9. Draw a series circuit that has four resistorsof 10, 20, 30, and 40 connected to a 6.0-V

battery.(a) Determine the total resistance and current. t (b) Find the voltage drop through the 30-

resistor. t

10. What is power and how is powerconsumption determined? k

CHAPTER 1211. What is a magnetic field? k

12. Explain why magnetic field lines cannotcross each other, even if they originate fromseparate magnets. k

13. Draw two uniform magnetic fields where one isstronger than the other. Label each field. k

14. Explain the effect that a magnetic field hason a current-carrying conductor when thereis no current. t

15. (a) Explain Oersteds principle. k (b) What effect did Oersteds observations have

on the study of electricity? k

E ACHIEVEMENT CHART CATEGORIESk Knowledge and understanding t Thinking and investigationc Communication a Application

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444 Unit E Review P

16. (a) Give two characteristics of the magneticfield created by a straight current-carryingconductor. k

(b) Give two characteristics of a magnetic fieldcreated by a solenoid. k

17. Describe the three factors that influencethe strength of a magnetic field in anelectromagnet. k

18. (a) Explain, in your own words, the motorprinciple. k

(b) Identify and explain the factors thatinfluence the motor principle. k

CHAPTER 1319. (a) Explain Faradays law of induction in your

own words. k (b) What is the significance of Faradays law? k

20. (a) Explain Lenzs law in your own words. c (b) How does Lenzs law work with

Faradays law? k

21. Explain the role of a generator in theproduction of electricity. k

22. Why are transformers used in the transmissionof electricity? k

23. Explain the difference between a step-uptransformer and a step-down transformer. k

Connect Your Understanding24. A charge of 68.0 C experiences a change in

potential energy of 5.0 102 J as it flowsthrough an electric relay. What is the electricalpotential difference of the relay? t

25. Determine the value of R 2 in the followingcircuit. t

Question 25

26. Determine the current through R 3 in thefollowing circuit. t

Question 26

27. (a) Redraw the following circuit to make anequivalent series circuit with two resistors:R 3 and R // . a

(b) A current of 50.0 mA flows through theammeter. What is the potential difference of the battery? t

(c) Determine the voltage drop through all theresistors. t

(d) Determine the current throughR

1 andR

2.t

(e) Determine the power dissipated by eachresistor. t

Question 27

28. Determine the voltage drop and the powerdissipated by each resistor in the followingdiagram. t

Question 28

29. Explain why two magnets in the same

orientation stored in a cabinet side-by-sidewould both weaken over time. t

30. Sketch the magnetic fields that would resultfrom the following magnet orientations. t

Question 30

31.

A bent rigid wire rests on a table in an externalmagnetic field that runs left to right. A 0.260 Acurrent moves through the wire as shown inthe diagram on the next page.(a) Wire segments AB and CD are both

30.0 cm long. Determine the magneticforce on segments AB and CD. t

(b) Determine the magnetic force on segmentBC. t

(c) If the mass of segment ABCD is 5.00 g, willthe wire lift off the table? t

R 1 5.0

R 3 8.0I 3.0 A

R 2 ?V T48.0 V

R 215.0

R 15.0

R 325.0

V T200.0 V

V T

R 15.0 k

R 220.0 k

R 3 2.0 k

R 1 6.0

R 2 3.0

R 3 4.0

I 10.0 A

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Unit E Review 447P

52. A magnet is dropped througha non-magnetic copper tube asshown below. Explain whateffect, if any, you would expectto see as the magnet falls. t

53. Give three different right-handrules that were explained inthis unit. Draw diagrams of the conductor, magnetic field,and force (if applicable) thatare associated with each rule. t

Revisit the Big Ideas andFundamental Concepts54. Explain how an understanding of the

relationship between electricity and magnetismwas built on various scientists observationsand experiments. t

55. Explain how the properties of magnetic fieldsand the flow of current make it possible toproduce and transmit electricity. t

Science, Technology, Society,and the Environment56. Explain why power transmission from a power

plant to distant cities requires the use of atransmission substation and distribution

substations. In your explanation, be sure todiscuss why the voltage during transmissionmust be very high mandating the use of alternating current instead of direct current. c

57. Copy the following table in your notebookand complete the information for the differentelectricity generation technologies discussed inthe text. t

58. Make a list of all the technologies that youuse that do not rely on the concepts of electromagnetism. What does this tell youabout electromagnetism? c

Reflection59. 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 youdid in this unit? Consider the way you work ingroups, as well as your individual work. c

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Method ofGeneratingElectricity

Is an ElectricGenerator Used?

Advantages andDisadvantages

Electricity Generating Methods

QuestionHow can you design and build a DC motor?

Task OverviewDC motors have revolutionized the way we live. Anelectric motor does not create any pollution and canoperate for years without maintenance. In this task, youwill use the concepts that you learned in this unit todesign and build a DC motor. The purpose of your motor

will be to lift as much weight as possible from the floorto a desk using 9.0 V. You will only be allowed to usematerials found in a local hardware store.

You will need to know how to wire series andparallel circuits, to understand the motor principle, andto understand how a simple DC motor is designed.Remember to completely design your motor before youbegin building.

Your teacher will provide you with a complete taskdescription.

Rev It Up!

Figure 13.35 A cross-section of a motor

Unit Task PHYSICS SOURCE E17

Question 52

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13 Physics 11se Ue End