Chapter 25 Current Resistance, and Electromotive Force

Size: px
Start display at page:

Download "Chapter 25 Current Resistance, and Electromotive Force"

Transcription

1 Chapter 25 Current Resistance, and Electromotive Force 1 Current In previous chapters we investigated the properties of charges at rest. In this chapter we want to investigate the properties of charges in motion. An electric current consists of charges in motion from one region to another. If the charges follow a conducting path that forms a closed loop, the path is called an electric circuit. 1.1 The direction of current flow When a constant, steady electric field E is established inside a conductor, the free electrons collectively move in a direction due to a steady force F = q E. Figure 1: This figure shows the random motion of electrons in a conductor without an E field. The second figure shows the collective motion of electrons in a conductor when an E field is present. 1

2 The collective motion of electrons in a conductor is characterized by their drift velocity v d. While the random motion of electrons has a very fast average speed of 10 6 m/s, the drift speed is very slow, often on the order of 10 4 m/s. The electric field is set up throughout the conductor at velocities approaching the speed of light, v c. Figure 2: The first figure (a) shows the direction of the conventional current, the flow of positive charges. The second figure (b) shows the flow of electrons in a metallic conducting moving in the opposite direction with respect to the current. 2

3 1.2 Current, Drift Velocity, and Current Density I = Q T = dq dt (the definition of current) (1) Figure 3: The current I is the time rate of charge transfer through the cross-sectional area A. The current is in the same direction as E. dq = q(nav d dt) = nqv d A dt I = dq dt = nqv d A The current per unit cross-sectional area is called the current density J: J = I A = nqv d (the current density) (2) J = nq v d (the current density in vector form) (3) 3

4 2 Resistivity The current density J in a conductor depends on the electric field E and on the properties of the material. The dependence can be quite complex, but for some materials, especially metals at a given temperature, J is nearly directly proportional to E, and the ratio of the magnitudes of E and J is constant. When materials exhibit this kind of behavior, it is said that they follow Ohm s Law. J = σ E = 1 ρ E (4) where σ is the conductivity and ρ is the resistivity shown in the table. Figure 4: This table shows the resistivities of various materials at room temperature (20 o C) 4

5 2.1 Resistivity and Temperature Figure 5: These figures show how the resistivity depends with the absolute temperature T for (a) a normal metal, (b) a semiconductor, and (c) a superconductor. The temperature dependence of the resistivity ρ can be written as: ρ(t ) = ρ o [1 + α (T T o )] (5) where α is the temperature coefficient of resistivity. 5

6 Figure 6: This table shows the coefficient of resistivities for various materials near room temperature. 3 Resistance For a conductor with resistivity ρ, the current density J and the electric field is E are related by the following equation: E = ρ J (6) Figure 7: This figure shows a conductor with uniform cross sectional area A. The current density is uniform over any cross section, and the electric field is constant along the length. Let V bet the potential difference between higher-potential and the lower-potential ends of the conductor, so that V is positive. V is the voltage across the con- 6

7 ductor. The direction of the current is always from the higher-potential to the lower-potential end. We can also relate the value of the current I to the potential difference between the ends of the conductor. Using the definition of current density J, we can write the current as I = JA. Likewise, the potential difference V between the ends is V = EL. Rewriting Eq. 6 above, we find: V L = ρi A or V = ( ) ρl A The ratio of V to I for a particular conductor is called its resistance R: I R = V I or V = IR (Ohm s Law) (7) We identify the resistance R to be R = ρl/a. 7

8 3.1 Interpreting Resistance Figure 8: This resistor has a resistance of 57 kω with an accuracy (tolerance) of ±10%. This is assuming that the color of the 3rd band is orange. Figure 9: This table shows the color codes used for labeling the resistances of resistors. The Resistance is Dependent Upon Temperature R(T ) = R o [1 + α (T T o )] where T 0 is often taken to be 0 o C or 20 o C. The temperature coefficient of resistance is represented by α, and the change in resistance is R 0 α(t T 0 ). 8

9 Figure 10: This figure shows the current-voltage relationships for two devices. In figure (a) the resistor obeys Ohm s law and the current I is proportional to the voltage V. In figure (b), a semiconductor diode, the current rises steeply with a modest amount of voltage, and the current flows only in the positive direction. 4 Electromotive Force and Circuits In order for a conductor to have a steady current, it must be part of a path that forms a closed loop or complete circuit. Otherwise, opposite charges would eventually build up on the two ends and negate the E field that produced the initial separation of charges. 9

10 Figure 11: This figure demonstrates why a steady current cannot persist in a section of conductor with a constant external E-field unless it is part of a circuit. Charges eventually accumulate on the two ends of the wire ultimately reducing the E field to E 0. J = 1 ρ E. 10

11 4.1 Electromotive Force In order to produce a steady current in a circuit, there has to be a device somewhere that acts to raise the potential (measured in volts) from low potential to high potential. Although in the circuit the electrostatic force is trying to push positive charge from high potential to low potential, the device that raises the potential pushes positive charges in the opposite sense (i.e., from low potential to high potential). Thus, the device must provide a force not derived from electrostatic means, buy by some other process. The non-electrostatic force that raises the voltage in a circuit is called an electromotive force, or emf, and is many times written as E. Figure 12: This is a schematic diagram of a source of emf (E) in an open-circuit situation. The electric-field force F e = q E and the nonelectrostatic force F n are shown acting on a positive charge q. The voltage across the battery terminals not connected. The most common source of emf is called a battery which uses an electrochemical process to move charge from low potential to high potential. When the battery is not connected, the voltage measured across the terminals is V ab = E. V ab = E Voltage measured across the battery not connected 11

12 Figure 13: This is schematic diagram of an ideal emf source in a complete circuit. The electric-field force F e = q E and the nonelectrostatic force F n are shown for a positive charge q. The current is in the direction from a to b in the external circuit and from b to a within the source. 12

13 4.2 Internal Resistance When the battery is connected to a simple circuit as shown in Fig. 13, current begins to flow through the whole circuit, including the battery. Because there is a small internal resistance r inside the battery, there is a slight voltage drop measured at the battery terminal V ab = E Ir. V ab = E Ir Voltage measured across the battery when connected 4.3 Symbols for Circuit Diagrams Figure 14: This table shows the common symbols found in a a circuit diagram. 13

14 4.4 Potential Changes around a Circuit Figure 15: This figure shows the potential rises and drops in a circuit. 14

15 5 Energy and Power in Electric Circuits When a charge q passes through a circuit element, there is a change in potential energy equal to qv ab. The potential energy decreases as the charge falls from potential V a to a lower potential V b. However, the moving charge does not gain kinetic energy (because there is conservation of charge and flux current is constant). In electric circuits we are more interested in the rate at which energy is either delivered to, or extracted from, a circuit element. If the current through the element is I, then a charge dq = I dt passes through the element in a time interval dt. The change in potential energy for this amount of charge crossing a potential difference V ab is du = V ab dq = V ab I dt. The power delivered to the circuit element must be Power = du dt = V ab I (power delivered to a circuit element) (8) Figure 16: This figure shows the power input to the circuit element between a and b. P = (V a V b )I = V ab I. 5.1 Power Input to a Pure Resistance Power = V I = V 2 R = I 2 R (9) 15

16 5.2 Power Output of a Source Figure 17: This figure shows the energy conversion in a simple circuit. Power output of a source a battery Power = V ab I = (E Ir)I = EI I 2 r 16

17 5.3 Power Input to a Source Figure 18: This figure shows two sources connected in a simple loop circuit. The source with the large emf delivers energy to the other source. Power input to a source a battery Power = V ab I = (E + Ir)I = EI + I 2 r 17

Chapter 25 Current, Resistance, and Electromotive Force

Chapter 25 Current, Resistance, and Electromotive Force Chapter 25 Current, Resistance, and Electromotive Force Lecture by Dr. Hebin Li Goals for Chapter 25 To understand current and how charges move in a conductor To understand resistivity and conductivity

More information

Flow Rate is the NET amount of water passing through a surface per unit time

Flow Rate is the NET amount of water passing through a surface per unit time Electric Current An Analogy Water Flow in a Pipe H 2 0 gallons/minute Flow Rate is the NET amount of water passing through a surface per unit time Individual molecules are bouncing around with speeds of

More information

Physics for Scientists & Engineers 2

Physics for Scientists & Engineers 2 Review The resistance R of a device is given by Physics for Scientists & Engineers 2 Spring Semester 2005 Lecture 8 R =! L A ρ is resistivity of the material from which the device is constructed L is the

More information

Chapter 28. Direct Current Circuits

Chapter 28. Direct Current Circuits Chapter 28 Direct Current Circuits Circuit Analysis Simple electric circuits may contain batteries, resistors, and capacitors in various combinations. For some circuits, analysis may consist of combining

More information

Physics 142 Steady Currents Page 1. Steady Currents

Physics 142 Steady Currents Page 1. Steady Currents Physics 142 Steady Currents Page 1 Steady Currents If at first you don t succeed, try, try again. Then quit. No sense being a damn fool about it. W.C. Fields Electric current: the slow average drift of

More information

Chapter 25: Electric Current

Chapter 25: Electric Current Chapter 25: Electric Current Conductors and Charge Carriers Consider a conducting piece of metal: The valence electrons are weakly bound to the nuclei form a fluidlike sea of electrons that can move through

More information

Chapter 26 & 27. Electric Current and Direct- Current Circuits

Chapter 26 & 27. Electric Current and Direct- Current Circuits Chapter 26 & 27 Electric Current and Direct- Current Circuits Electric Current and Direct- Current Circuits Current and Motion of Charges Resistance and Ohm s Law Energy in Electric Circuits Combination

More information

Chapter 3: Electric Current and Direct-Current Circuit

Chapter 3: Electric Current and Direct-Current Circuit Chapter 3: Electric Current and Direct-Current Circuit n this chapter, we are going to discuss both the microscopic aspect and macroscopic aspect of electric current. Direct-current is current that flows

More information

Chapter 24: Electric Current

Chapter 24: Electric Current Chapter 24: Electric Current Current Definition of current A current is any motion of charge from one region to another. Suppose a group of charges move perpendicular to surface of area A. The current

More information

fehmibardak.cbu.tr Temporary Office 348, Mühendislik Fakültesi B Blok

fehmibardak.cbu.tr Temporary Office 348, Mühendislik Fakültesi B Blok fehmibardak.cbu.tr Temporary Office 348, Mühendislik Fakültesi B Blok 1 Course Progress Introductory level Electrostatic, Coulomb s Law Electric Field, Gauss Law Magnetic field, Maxwell s Equations Current,

More information

M. C. Escher: Waterfall. 18/9/2015 [tsl425 1/29]

M. C. Escher: Waterfall. 18/9/2015 [tsl425 1/29] M. C. Escher: Waterfall 18/9/2015 [tsl425 1/29] Direct Current Circuit Consider a wire with resistance R = ρl/a connected to a battery. Resistor rule: In the direction of I across a resistor with resistance

More information

Chapter 3: Electric Current And Direct-Current Circuits

Chapter 3: Electric Current And Direct-Current Circuits Chapter 3: Electric Current And Direct-Current Circuits 3.1 Electric Conduction 3.1.1 Describe the microscopic model of current Mechanism of Electric Conduction in Metals Before applying electric field

More information

Chapter 24: Electric Current

Chapter 24: Electric Current Chapter 24: Electric Current Electric current Electric current is a net flow of electric charge. Quantitatively, current is the rate at which charge crosses a given area. I = dq dt dq = q(n AL)=q(n Av

More information

Direct Currents. We will now start to consider charges that are moving through a circuit, currents. Sunday, February 16, 2014

Direct Currents. We will now start to consider charges that are moving through a circuit, currents. Sunday, February 16, 2014 Direct Currents We will now start to consider charges that are moving through a circuit, currents. 1 Direct Current Current usually consists of mobile electrons traveling in conducting materials Direct

More information

AP Physics C - E & M

AP Physics C - E & M Slide 1 / 27 Slide 2 / 27 AP Physics C - E & M Current, Resistance & Electromotive Force 2015-12-05 www.njctl.org Slide 3 / 27 Electric Current Electric Current is defined as the movement of charge from

More information

By Mir Mohammed Abbas II PCMB 'A' CHAPTER FORMULAS & NOTES. 1. Current through a given area of a conductor is the net charge passing

By Mir Mohammed Abbas II PCMB 'A' CHAPTER FORMULAS & NOTES. 1. Current through a given area of a conductor is the net charge passing Formulae For u CURRENT ELECTRICITY 1 By Mir Mohammed Abbas II PCMB 'A' 1 Important Terms, Definitions & Formulae CHAPTER FORMULAS & NOTES 1. Current through a given area of a conductor is the net charge

More information

Chapters 24/25: Current, Circuits & Ohm s law Thursday September 29 th **Register your iclickers**

Chapters 24/25: Current, Circuits & Ohm s law Thursday September 29 th **Register your iclickers** Chapters 24/25: Current, Circuits & Ohm s law Thursday September 29 th **Register your iclickers** Conductors under dynamic conditions Current, current density, drift velocity Ohm s law Types of conductor

More information

Current and Resistance

Current and Resistance Chapter 26 Current and Resistance Copyright 26-1 Electric Current As Fig. (a) reminds us, any isolated conducting loop regardless of whether it has an excess charge is all at the same potential. No electric

More information

CURRENT ELECTRICITY CHAPTER 13 CURRENT ELECTRICITY Qs. Define Charge and Current. CHARGE Definition Flow of electron is known as Charge. It is denoted by Q. Unit Its unit is Coulomb. 1 Coulomb = 10(-6)

More information

Electric Currents. Resistors (Chapters 27-28)

Electric Currents. Resistors (Chapters 27-28) Electric Currents. Resistors (Chapters 27-28) Electric current I Resistance R and resistors Relation between current and resistance: Ohm s Law Resistivity ρ Energy dissipated by current. Electric power

More information

Current and Resistance

Current and Resistance Current and Resistance 1 Define the current. Understand the microscopic description of current. Discuss the rat at which the power transfer to a device in an electric current. 2 2-1 Electric current 2-2

More information

What is an Electric Current?

What is an Electric Current? Electric Circuits NTODUCTON: Electrical circuits are part of everyday human life. e.g. Electric toasters, electric kettle, electric stoves All electrical devices need electric current to operate. n this

More information

Chapter 27. Current and Resistance

Chapter 27. Current and Resistance Chapter 27 Current and Resistance Electric Current Most practical applications of electricity deal with electric currents. The electric charges move through some region of space. The resistor is a new

More information

Electric Current. Electric current is the rate of flow of charge through some region of space The SI unit of current is the ampere (A)

Electric Current. Electric current is the rate of flow of charge through some region of space The SI unit of current is the ampere (A) Electric Current Electric current is the rate of flow of charge through some region of space The SI unit of current is the ampere (A) 1 A = 1 C / s The symbol for electric current is I Average Electric

More information

Chapter 18. Direct Current Circuits

Chapter 18. Direct Current Circuits Chapter 18 Direct Current Circuits Sources of emf The source that maintains the current in a closed circuit is called a source of emf Any devices that increase the potential energy of charges circulating

More information

Electric Currents & Resistance

Electric Currents & Resistance Electric Currents & Resistance Electric Battery A battery produces electricity by transforming chemical energy into electrical energy. The simplest battery contains two plates or rods made of dissimilar

More information

Chapter 17. Current and Resistance. Sections: 1, 3, 4, 6, 7, 9

Chapter 17. Current and Resistance. Sections: 1, 3, 4, 6, 7, 9 Chapter 17 Current and Resistance Sections: 1, 3, 4, 6, 7, 9 Equations: 2 2 1 e r q q F = k 2 e o r Q k q F E = = I R V = A L R ρ = )] ( 1 [ o o T T + = α ρ ρ V I V t Q P = = R V R I P 2 2 ) ( = = C Q

More information

Chapter 17 Electric Current and Resistance Pearson Education, Inc.c

Chapter 17 Electric Current and Resistance Pearson Education, Inc.c Chapter 17 Electric Current and Resistance 2010 Pearson Education, Inc.c 1 Units of Chapter 17 Batteries and Direct Current Current and Drift Velocity Resistance and Ohm s Law Electric Power 2010 Pearson

More information

Chapter 27 Current and Resistance 27.1 Electric Current

Chapter 27 Current and Resistance 27.1 Electric Current Chapter 27 Current and esistance 27.1 Electric Current Electric current: dq dt, unit: ampere 1A = 1C s The rate at which charge flows through a surface. No longer have static equilibrium. E and Q can 0

More information

Chapter 2. Engr228 Circuit Analysis. Dr Curtis Nelson

Chapter 2. Engr228 Circuit Analysis. Dr Curtis Nelson Chapter 2 Engr228 Circuit Analysis Dr Curtis Nelson Chapter 2 Objectives Understand symbols and behavior of the following circuit elements: Independent voltage and current sources; Dependent voltage and

More information

Ohm's Law and Resistance

Ohm's Law and Resistance Ohm's Law and Resistance Resistance Resistance is the property of a component which restricts the flow of electric current. Energy is used up as the voltage across the component drives the current through

More information

Physics 201. Professor P. Q. Hung. 311B, Physics Building. Physics 201 p. 1/3

Physics 201. Professor P. Q. Hung. 311B, Physics Building. Physics 201 p. 1/3 Physics 201 p. 1/3 Physics 201 Professor P. Q. Hung 311B, Physics Building Physics 201 p. 2/3 Summary of last lecture Equipotential surfaces: Surfaces where the potential is the same everywhere, e.g. the

More information

Chapter 21 Electric Current and Direct- Current Circuits

Chapter 21 Electric Current and Direct- Current Circuits Chapter 21 Electric Current and Direct- Current Circuits 1 Overview of Chapter 21 Electric Current and Resistance Energy and Power in Electric Circuits Resistors in Series and Parallel Kirchhoff s Rules

More information

Lecture Outline Chapter 21. Physics, 4 th Edition James S. Walker. Copyright 2010 Pearson Education, Inc.

Lecture Outline Chapter 21. Physics, 4 th Edition James S. Walker. Copyright 2010 Pearson Education, Inc. Lecture Outline Chapter 21 Physics, 4 th Edition James S. Walker Chapter 21 Electric Current and Direct- Current Circuits Units of Chapter 21 Electric Current Resistance and Ohm s Law Energy and Power

More information

EXPERIMENT 12 OHM S LAW

EXPERIMENT 12 OHM S LAW EXPERIMENT 12 OHM S LAW INTRODUCTION: We will study electricity as a flow of electric charge, sometimes making analogies to the flow of water through a pipe. In order for electric charge to flow a complete

More information

Physics 169. Luis anchordoqui. Kitt Peak National Observatory. Wednesday, March 8, 17

Physics 169. Luis anchordoqui. Kitt Peak National Observatory. Wednesday, March 8, 17 Physics 169 Kitt Peak National Observatory Luis anchordoqui 1 5.1 Ohm s Law and Resistance ELECTRIC CURRENT is defined as flow of electric charge through a cross-sectional area Convention i = dq dt Unit

More information

Chapter 27. Current And Resistance

Chapter 27. Current And Resistance Chapter 27 Current And Resistance Electric Current Electric current is the rate of flow of charge through some region of space The SI unit of current is the ampere (A) 1 A = 1 C / s The symbol for electric

More information

Physics 202: Lecture 5, Pg 1

Physics 202: Lecture 5, Pg 1 Resistance Resistors Series Parallel Ohm s law Electric Circuits Current Physics 132: Lecture e 15 Elements of Physics II Kirchhoff s laws Agenda for Today Physics 202: Lecture 5, Pg 1 Electric Current

More information

PHY102 Electricity Course Summary

PHY102 Electricity Course Summary TOPIC 1 ELECTOSTTICS PHY1 Electricity Course Summary Coulomb s Law The magnitude of the force between two point charges is directly proportional to the product of the charges and inversely proportional

More information

Chapter 27. Current And Resistance

Chapter 27. Current And Resistance Chapter 27 Current And Resistance Electric Current Electric current is the rate of flow of charge through some region of space The SI unit of current is the ampere (A) 1 A = 1 C / s The symbol for electric

More information

Chapter 16. Current and Drift Speed. Electric Current, cont. Current and Drift Speed, cont. Current and Drift Speed, final

Chapter 16. Current and Drift Speed. Electric Current, cont. Current and Drift Speed, cont. Current and Drift Speed, final Chapter 6 Current, esistance, and Direct Current Circuits Electric Current Whenever electric charges of like signs move, an electric current is said to exist The current is the rate at which the charge

More information

Objective of Lecture Discuss resistivity and the three categories of materials Chapter 2.1 Show the mathematical relationships between charge,

Objective of Lecture Discuss resistivity and the three categories of materials Chapter 2.1 Show the mathematical relationships between charge, Objective of Lecture Discuss resistivity and the three categories of materials Chapter 2.1 Show the mathematical relationships between charge, current, voltage, and energy. Chapter 2.2-2.4 Define resistance

More information

Chapter 3: Current and Resistance. Direct Current Circuits

Chapter 3: Current and Resistance. Direct Current Circuits Chapter 3: Current and Resistance. Direct Current Circuits 3.1. Electric Current 3.2. Resistance and Resistivity 3.3. Ohm s Law and a Microscopic View of Ohm s Law 3.4. Semiconductors and Superconductors

More information

Class 8. Resistivity and Resistance Circuits. Physics 106. Winter Press CTRL-L to view as a slide show. Class 8. Physics 106.

Class 8. Resistivity and Resistance Circuits. Physics 106. Winter Press CTRL-L to view as a slide show. Class 8. Physics 106. and Circuits and Winter 2018 Press CTRL-L to view as a slide show. Last time we learned about Capacitance Problems Parallel-Plate Capacitors Capacitors in Circuits Current Ohm s Law and Today we will learn

More information

XII PHYSICS [CURRENT ELECTRICITY] CHAPTER NO. 13 LECTURER PHYSICS, AKHSS, K.

XII PHYSICS [CURRENT ELECTRICITY] CHAPTER NO. 13 LECTURER PHYSICS, AKHSS, K. XII PHYSICS LECTURER PHYSICS, AKHSS, K affan_414@live.com https://promotephysics.wordpress.com [CURRENT ELECTRICITY] CHAPTER NO. 13 CURRENT Strength of current in a conductor is defined as, Number of coulombs

More information

Capacitance. A different kind of capacitor: Work must be done to charge a capacitor. Capacitors in circuits. Capacitor connected to a battery

Capacitance. A different kind of capacitor: Work must be done to charge a capacitor. Capacitors in circuits. Capacitor connected to a battery Capacitance The ratio C = Q/V is a conductor s self capacitance Units of capacitance: Coulomb/Volt = Farad A capacitor is made of two conductors with equal but opposite charge Capacitance depends on shape

More information

Physics 1214 Chapter 19: Current, Resistance, and Direct-Current Circuits

Physics 1214 Chapter 19: Current, Resistance, and Direct-Current Circuits Physics 1214 Chapter 19: Current, Resistance, and Direct-Current Circuits 1 Current current: (also called electric current) is an motion of charge from one region of a conductor to another. Current When

More information

Electric Currents and Circuits

Electric Currents and Circuits Nicholas J. Giordano www.cengage.com/physics/giordano Chapter 19 Electric Currents and Circuits Marilyn Akins, PhD Broome Community College Electric Circuits The motion of charges leads to the idea of

More information

Electric Current. Chapter 17. Electric Current, cont QUICK QUIZ Current and Resistance. Sections: 1, 3, 4, 6, 7, 9

Electric Current. Chapter 17. Electric Current, cont QUICK QUIZ Current and Resistance. Sections: 1, 3, 4, 6, 7, 9 Electric Current Chapter 17 Current and Resistance Sections: 1, 3, 4, 6, 7, 9 Whenever electric charges of like signs move, an electric current is said to exist The current is the rate at which the charge

More information

Chapter 28. Direct Current Circuits

Chapter 28. Direct Current Circuits Chapter 28 Direct Current Circuits Electromotive Force An electromotive force device, or emf device, is a source of constant potential. The emf describes the work done per unit charge and has units of

More information

RESISTANCE AND NETWORKS

RESISTANCE AND NETWORKS PURPOSE The purpose of this laboratory is to learn to construct simple circuits; and, to become familiar with the use of power supplies and the digital multimeter. to experimentally find the equivalent

More information

Version 001 CIRCUITS holland (1290) 1

Version 001 CIRCUITS holland (1290) 1 Version CIRCUITS holland (9) This print-out should have questions Multiple-choice questions may continue on the next column or page find all choices before answering AP M 99 MC points The power dissipated

More information

Look over Chapter 26 sections 1-7 Examples 3, 7. Look over Chapter 18 sections 1-5, 8 over examples 1, 2, 5, 8, 9,

Look over Chapter 26 sections 1-7 Examples 3, 7. Look over Chapter 18 sections 1-5, 8 over examples 1, 2, 5, 8, 9, Look over Chapter 26 sections 1-7 Examples 3, 7 Look over Chapter 18 sections 1-5, 8 over examples 1, 2, 5, 8, 9, 1)How to find a current in a wire. 2)What the Current Density and Draft Speed are. 3)What

More information

Chapter 25. Electromotive Force. PowerPoint Lectures for University Physics, Twelfth Edition Hugh D. Young and Roger A. Freedman

Chapter 25. Electromotive Force. PowerPoint Lectures for University Physics, Twelfth Edition Hugh D. Young and Roger A. Freedman Chapter 25 Current, Resistance, and Electromotive Force PowerPoint Lectures for University Physics, Twelfth Edition Hugh D. Young and Roger A. Freedman Lectures by James Pazun Main points (I, R, emf) 1.

More information

Current and Resistance. February 12, 2014 Physics for Scientists & Engineers 2, Chapter 25 1

Current and Resistance. February 12, 2014 Physics for Scientists & Engineers 2, Chapter 25 1 Current and Resistance February 12, 2014 Physics for Scientists & Engineers 2, Chapter 25 1 Helproom hours! Strosacker learning center, BPS 1248! Mo: 10am noon, 1pm 9pm! Tue: noon 6pm! We: noon 2pm! Th:

More information

Let s go to something more concrete

Let s go to something more concrete Let s go to something more concrete Let me define an electric current Whenever charges of like sign are moving, an electric current exists Suppose I have a surface A with charges (assume + because of Franklin

More information

Electric Current. You must know the definition of current, and be able to use it in solving problems.

Electric Current. You must know the definition of current, and be able to use it in solving problems. Today s agenda: Electric Current. You must know the definition of current, and be able to use it in solving problems. Current Density. You must understand the difference between current and current density,

More information

Lesson 8 Electrical Properties of Materials. A. Definition: Current is defined as the rate at which charge flows through a surface:

Lesson 8 Electrical Properties of Materials. A. Definition: Current is defined as the rate at which charge flows through a surface: Lesson 8 Electrical Properties of Materials I. Current I A. Definition: Current is defined as the rate at which charge flows through a surface: + + B. Direction: The direction of positive current flow

More information

Resistance Learning Outcomes. Resistance Learning Outcomes. Resistance

Resistance Learning Outcomes. Resistance Learning Outcomes. Resistance Resistance Learning Outcomes Define resistance and give its unit. Solve problems about resistance. State Ohm s Law. HL: Derive the formulas for resistors in series and parallel. Solve problems about resistors

More information

Chapter 20 Electric Circuits

Chapter 20 Electric Circuits Chapter 0 Electric Circuits Chevy olt --- Electric vehicle of the future Goals for Chapter 9 To understand the concept of current. To study resistance and Ohm s Law. To observe examples of electromotive

More information

Chapter 27. Current and Resistance

Chapter 27. Current and Resistance Chapter 27 Current and Resistance Electric Current Most practical applications of electricity deal with electric currents. The electric charges move through some region of space. The resistor is a new

More information

and in a simple circuit Part 2

and in a simple circuit Part 2 Current, Resistance, and Voltage in a simple circuit Part 2 Electric Current Whenever electric charges of like signs move, an electric current is said to exist. Look at the charges flowing perpendicularly

More information

Chapter 7 Direct-Current Circuits

Chapter 7 Direct-Current Circuits Chapter 7 Direct-Current Circuits 7. Introduction... 7. Electromotive Force... 7.3 Resistors in Series and in Parallel... 4 7.4 Kirchhoff s Circuit Rules... 6 7.5 Voltage-Current Measurements... 8 7.6

More information

General Physics (PHY 2140)

General Physics (PHY 2140) General Physics (PHY 2140) Lecture 9 Electrodynamics Electric current temperature variation of resistance electrical energy and power http://www.physics.wayne.edu/~apetrov/phy2140/ Chapter 17-18 1 Department

More information

Chapter 25 Electric Currents and Resistance. Copyright 2009 Pearson Education, Inc.

Chapter 25 Electric Currents and Resistance. Copyright 2009 Pearson Education, Inc. Chapter 25 Electric Currents and Resistance 25-4 Resistivity Example 25-5: Speaker wires. Suppose you want to connect your stereo to remote speakers. (a) If each wire must be 20 m long, what diameter copper

More information

Direct Current Circuits. February 18, 2014 Physics for Scientists & Engineers 2, Chapter 26 1

Direct Current Circuits. February 18, 2014 Physics for Scientists & Engineers 2, Chapter 26 1 Direct Current Circuits February 18, 2014 Physics for Scientists & Engineers 2, Chapter 26 1 Kirchhoff s Junction Rule! The sum of the currents entering a junction must equal the sum of the currents leaving

More information

AC vs. DC Circuits. Constant voltage circuits. The voltage from an outlet is alternating voltage

AC vs. DC Circuits. Constant voltage circuits. The voltage from an outlet is alternating voltage Circuits AC vs. DC Circuits Constant voltage circuits Typically referred to as direct current or DC Computers, logic circuits, and battery operated devices are examples of DC circuits The voltage from

More information

6 Chapter. Current and Resistance

6 Chapter. Current and Resistance 6 Chapter Current and Resistance 6.1 Electric Current... 6-2 6.1.1 Current Density... 6-2 6.2 Ohm s Law... 6-5 6.3 Summary... 6-8 6.4 Solved Problems... 6-9 6.4.1 Resistivity of a Cable... 6-9 6.4.2 Charge

More information

9/22/16 ANNOUNCEMENT ANNOUNCEMENT FINAL EXAM

9/22/16 ANNOUNCEMENT ANNOUNCEMENT FINAL EXAM ANNOUNCEMENT Exam 1: Tuesday September 27, 2016, 8 PM 10 PM Location: Elliot Hall of Music Covers all readings, lectures, homework from Chapters 21 through 23 Multiple choice (1518 questions) Practice

More information

To receive full credit, you must show all your work (including steps taken, calculations, and formulas used).

To receive full credit, you must show all your work (including steps taken, calculations, and formulas used). Page 1 Score Problem 1: (35 pts) Problem 2: (25 pts) Problem 3: (25 pts) Problem 4: (25 pts) Problem 5: (15 pts) TOTAL: (125 pts) To receive full credit, you must show all your work (including steps taken,

More information

AP Physics C. Electric Circuits III.C

AP Physics C. Electric Circuits III.C AP Physics C Electric Circuits III.C III.C.1 Current, Resistance and Power The direction of conventional current Suppose the cross-sectional area of the conductor changes. If a conductor has no current,

More information

A free web support in Education. Internal resistance of the battery, r = 3 Ω. Maximum current drawn from the battery = I According to Ohm s law,

A free web support in Education. Internal resistance of the battery, r = 3 Ω. Maximum current drawn from the battery = I According to Ohm s law, Exercises Question 3.1: The storage battery of a car has an emf of 12 V. If the internal resistance of the battery is 0.4Ω, what is the maximum current that can be drawn from the battery? Answer 3.1: Emf

More information

1 Written and composed by: Prof. Muhammad Ali Malik (M. Phil. Physics), Govt. Degree College, Naushera

1 Written and composed by: Prof. Muhammad Ali Malik (M. Phil. Physics), Govt. Degree College, Naushera CURRENT ELECTRICITY Q # 1. What do you know about electric current? Ans. Electric Current The amount of electric charge that flows through a cross section of a conductor per unit time is known as electric

More information

Chapter 28 Solutions

Chapter 28 Solutions Chapter 8 Solutions 8.1 (a) P ( V) R becomes 0.0 W (11.6 V) R so R 6.73 Ω (b) V IR so 11.6 V I (6.73 Ω) and I 1.7 A ε IR + Ir so 15.0 V 11.6 V + (1.7 A)r r 1.97 Ω Figure for Goal Solution Goal Solution

More information

PHYS 1444 Section 002 Lecture #13

PHYS 1444 Section 002 Lecture #13 PHYS 1444 Section 002 Lecture #13 Monday, Oct. 16, 2017 Dr. Animesh Chatterjee (disguising as Dr. Yu) Chapter 25 Electric Current Ohm s Law: Resisters, Resistivity Electric Power Alternating Current Microscopic

More information

Resistance Learning Outcomes

Resistance Learning Outcomes Resistance Learning Outcomes Define resistance and give its unit. Solve problems about resistance. State Ohm s Law. HL: Derive the formulas for resistors in series and parallel. Solve problems about resistors

More information

PHYS 1444 Section 004 Lecture #10

PHYS 1444 Section 004 Lecture #10 PHYS 1444 Section 004 Lecture #10 Dr. Electric Current and Resistance The Battery Ohm s Law: Resisters Resistivity Electric Power Alternating Current Power Delivered by AC Today s homework is #6, due 10pm,

More information

Chapter 25 Electric Currents and. Copyright 2009 Pearson Education, Inc.

Chapter 25 Electric Currents and. Copyright 2009 Pearson Education, Inc. Chapter 25 Electric Currents and Resistance 25-1 The Electric Battery Volta discovered that electricity could be created if dissimilar metals were connected by a conductive solution called an electrolyte.

More information

University Physics (PHY 2326)

University Physics (PHY 2326) Chapter 25 University Physics (PHY 2326) Lecture 7 Electrostatics and electrodynamics Capacitance and capacitors capacitors with dielectrics Electric current current and drift speed resistance and Ohm

More information

Where k = 1. The electric field produced by a point charge is given by

Where k = 1. The electric field produced by a point charge is given by Ch 21 review: 1. Electric charge: Electric charge is a property of a matter. There are two kinds of charges, positive and negative. Charges of the same sign repel each other. Charges of opposite sign attract.

More information

Electric Currents and Simple Circuits

Electric Currents and Simple Circuits -1 Electric Currents and Simple Circuits Electrons can flow along inside a metal wire if there is an E-field present to push them along ( F= qe). The flow of electrons in a wire is similar to the flow

More information

ELEC 103. Objectives

ELEC 103. Objectives ELEC 103 Voltage, Current, and Resistance Objectives Define voltage and discuss its characteristics Define current and discuss its characteristics Define resistance and discuss its characteristics Identify

More information

Chapter 6 DIRECT CURRENT CIRCUITS. Recommended Problems: 6,9,11,13,14,15,16,19,20,21,24,25,26,28,29,30,31,33,37,68,71.

Chapter 6 DIRECT CURRENT CIRCUITS. Recommended Problems: 6,9,11,13,14,15,16,19,20,21,24,25,26,28,29,30,31,33,37,68,71. Chapter 6 DRECT CURRENT CRCUTS Recommended Problems: 6,9,,3,4,5,6,9,0,,4,5,6,8,9,30,3,33,37,68,7. RESSTORS N SERES AND N PARALLEL - N SERES When two resistors are connected together as shown we said that

More information

What are the two types of current? The two types of current are direct current and alternating current.

What are the two types of current? The two types of current are direct current and alternating current. Electric Current What are the two types of current? The two types of current are direct current and alternating current. Electric Current The continuous flow of electric charge is an electric current.

More information

This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 4.0 License.

This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 4.0 License. University of Rhode Island DigitalCommons@URI PHY 204: Elementary Physics II Physics Course Materials 2015 10. Resistors II Gerhard Müller University of Rhode Island, gmuller@uri.edu Creative Commons License

More information

Chapter 27. Circuits

Chapter 27. Circuits Chapter 27 Circuits 1 1. Pumping Chagres We need to establish a potential difference between the ends of a device to make charge carriers follow through the device. To generate a steady flow of charges,

More information

Lecture 6 Current and Resistance Ch. 26

Lecture 6 Current and Resistance Ch. 26 Lecture 6 Current and esistance Ch. 6 Cartoon -nvention of the battery and Voltaic Cell Warm-up problem Topics What is current? Current density Conservation of Current esistance Temperature dependence

More information

16.1 Electrical Current

16.1 Electrical Current 16.1 Electrical Current Electric Current Electric Current When the ends of an electric conductor are at different electric potentials, charge flows from one end to the other Flow of Charge Charge flows

More information

Electric Charge. Electric Charge ( q ) unbalanced charges positive and negative charges. n Units Coulombs (C)

Electric Charge. Electric Charge ( q ) unbalanced charges positive and negative charges. n Units Coulombs (C) Electric Charge Electric Charge ( q ) unbalanced charges positive and negative charges n Units Coulombs (C) Electric Charge How do objects become charged? Types of materials Conductors materials in which

More information

Inductance, RL Circuits, LC Circuits, RLC Circuits

Inductance, RL Circuits, LC Circuits, RLC Circuits Inductance, R Circuits, C Circuits, RC Circuits Inductance What happens when we close the switch? The current flows What does the current look like as a function of time? Does it look like this? I t Inductance

More information

Chapter 27 Current and resistance

Chapter 27 Current and resistance 27.1 Electric Current Chapter 27 Current and resistance 27.2 Resistance 27.3 A Model for Electrical Conduction 27.4 Resistance and Temperature 27.6 Electrical Power 2 27.1 Electric Current Consider a system

More information

52 VOLTAGE, CURRENT, RESISTANCE, AND POWER

52 VOLTAGE, CURRENT, RESISTANCE, AND POWER 52 VOLTAGE, CURRENT, RESISTANCE, AND POWER 1. What is voltage, and what are its units? 2. What are some other possible terms for voltage? 3. Batteries create a potential difference. The potential/voltage

More information

ET 162 Circuit Analysis. Current and Voltage. Electrical and Telecommunication Engineering Technology. Professor Jang

ET 162 Circuit Analysis. Current and Voltage. Electrical and Telecommunication Engineering Technology. Professor Jang ET 162 Circuit Analysis Current and Voltage Electrical and Telecommunication Engineering Technology Professor Jang Acknowledgement I want to express my gratitude to Prentice Hall giving me the permission

More information

PHYS 1444 Section 003. Lecture #12

PHYS 1444 Section 003. Lecture #12 Chapter 5 Power PHYS 1444 Section 003 Alternating Current Microscopic Current Chapter 6 EMF and Terminal Voltage Lecture #1 Tuesday October 9, 01 Dr. Andrew Brandt Resistors in Series and Parallel Energy

More information

CHAPTER 1 ELECTRICITY

CHAPTER 1 ELECTRICITY CHAPTER 1 ELECTRICITY Electric Current: The amount of charge flowing through a particular area in unit time. In other words, it is the rate of flow of electric charges. Electric Circuit: Electric circuit

More information

PHYS 1441 Section 001 Lecture #10 Tuesday, June 21, 2016

PHYS 1441 Section 001 Lecture #10 Tuesday, June 21, 2016 PHYS 1441 Section 001 Lecture #10 Tuesday, June 21, 2016 Chapter 25 Electric Current and Resistance The Battery Ohm s Law: Resisters, Resistivity Electric Power Alternating Current Microscopic View of

More information

Resistance, Ohm s Law and Kirchoff s Laws

Resistance, Ohm s Law and Kirchoff s Laws Universiti Teknologi MR Fakulti Sains Gunaan Resistance, Ohm s Law and Kirchoff s Laws PHY631: Physical Science ctivity Name: HP: Lab#: Intro Objectives The goal of today s activity is to physically investigate

More information

Physics 115. General Physics II. Session 24 Circuits Series and parallel R Meters Kirchoff s Rules

Physics 115. General Physics II. Session 24 Circuits Series and parallel R Meters Kirchoff s Rules Physics 115 General Physics II Session 24 Circuits Series and parallel R Meters Kirchoff s Rules R. J. Wilkes Email: phy115a@u.washington.edu Home page: http://courses.washington.edu/phy115a/ 5/15/14 Phys

More information

Electricity. Lily, Laura, Lynette, Elyse, Gillian, Emma, Hailey Period 2. onedio.com

Electricity. Lily, Laura, Lynette, Elyse, Gillian, Emma, Hailey Period 2. onedio.com Electricity Lily, Laura, Lynette, Elyse, Gillian, Emma, Hailey Period 2 onedio.com Electrostatics vs. Electricity Electrostatics is the study of charges at rest Electrostatics: to help remember the difference

More information

Chapter 27: Current and Resistance

Chapter 27: Current and Resistance Chapter 7: Current and esistance In this section of the course we will be studying the flow of electric charge, current, in a circuit. We have already seen electric current when we first discussed electric

More information