Physics III PH 113
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This 39 page Class Notes was uploaded by Jalon Willms on Monday October 19, 2015. The Class Notes belongs to PH 113 at Rose-Hulman Institute of Technology taught by Renat Letfullin in Fall. Since its upload, it has received 15 views. For similar materials see /class/225113/ph-113-rose-hulman-institute-of-technology in Physics 2 at Rose-Hulman Institute of Technology.
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Date Created: 10/19/15
Magnetism Lecture 02 Chapter 27 Syllabus is available online httpWWWr0sehulmaneduletfulli 11713 Physics 113 Dr Renat Letfullin l Todayquot 0 Magnetic Field 0 Source of Magnetic Fields 0 Magnetic Field Lines BiotSavart Law 39 Ampere s Experiment f g o Magnetic Force 7 Movie Magnetism quot5 Physiesns 39 we v 2 Conclusions from Experiments Concept Magnetism is not the same as electricity Magnetic poles are similar to charges but have important differences Magnetism is along range force The compass needle responds to the bar magnet from some distance away Magnets have two poles north and south Like poles repel and opposite poles attract Poles of a magnet can be identified with a compass A north magnet pole attracts the southseeking end of the compass needle which is a south pole Some materials stick to magnets and others do not The materials that are attracted are called magnetic materials Magnetic materials are attracted by either poe of a magnetPhysics 113 Dr Renat Letfullin 3 Magnetic field introduction One problem with the Magnetism Magnetic force is a long range force The compass needle reSponds to the bar magnet from some distance away What is a Field A FIELD is something that can be defined anywhere in space A field represents some physical quantity eg temperature wind speed force It can be a scalar field eg Temperature field It can be a vector field eg Electric field It can be a tensor field eg Spacetime curvature Physics 113 Dr Renat Letfullin 4 A Scalar Field These isolated temperatures sample the scalar eld you only learn the temperature at the point you choose but Tis defined everywhere as y Physias 113 A Vector Field It may be more interesting to know which way the wind is blowing That would require a vector field you learn both wind speed and direction Pharsias 113 6 Electric Field Physicists did not like the concept of action at a distance ie a force that was caused by an object a long distance away Thus rather than They preferred to think of an object producing a eld and other objects interacting with Physics 113 Dr Rena e u 39 Magnetic Field Bar magnet produces magnetic field Due to this field we can explain longrange interaction between magnets Source of Magnetic Fields What is the source of magnetic fields if not magnetic charge Answer electric charge in motion eg current in wire surrounding cylinder solenoid produces very similar field to that of bar magnet Orbits of electrons about nuclei Physics 113 Dr Renat Letfullin 9 The First Study 39 39 H Ch 1quot O 1 d of the Magnetlc Fleld ans lgsr39 mirs e In April of 1820 the Danish physicist Hans Christian Oersted was giving a evening lecture in which he was demonstrating the heating of a wire when an electrical current passed through it He noticed that a compass that was nearby on the table de ected each time he made the current ow Until that time physicists had considered electricity and magnetism to be unrelated phenomena Oersted discovered that the missing link between electricity and magnetism was the electric current Physics 113 Dr Renat Letfullin Electric current and magnets R 1en U16 ire cuniesxn E cuntnthc conuw pohns th e ec on Source of Magnetic Fields What is the source of magnetic fields if not magnetic charge Answer electric charge in motion eg current in wire surrounding cylinder solenoid produces very similar field to that of bar magnet Therefore understanding source of field generated by bar magnet lies in understanding currents at atomic level within bulk matter Intrinsic spin of electrons more important effect 12 Physics 113 Dr Renat Le ullin Direction of the Magnetic Field 39I39h Current 4W Hum 10 1 Thumb of gin hand 39 L f 1 4oiming in direction carrymg umunu lhu 1m P 0139 curmm direction your fingers are pointin J 1 MA MA1 W 7 JIMms Ad Vector Conventions 9 I Current inlo page 5 Vectors into page Current into page 9 Vectors out of page Current out of page Clicker Question P I The magne ric field a r poin r P poin rs 0 Up b Down c Righ39r d Info The page e OUT of The page Physics 113 Dr Renat Letfullin 15 Magnetic Field Lines mip Magnetic fieici lines are circles around the Wirts Thc magnetic field vectors are tangent to circles around the wire pointing in the direction cn by he right h id rule The eld is weaker farther from the wn 7 Currentcarrying wire mii39m Ai V W I A A J Magnetic eld lines may be traced Magnetic eld lines may be traced from N toward S in analogous fashion to the electric eld lines At each point the field line is tangent to the magnetic field vector B At each point the field lines point in the same direction a compass would The more dense y the field lines are packed the stronger the field is at that point therefore magnetic field lines point away from N poles and toward S poles The Magnetic Field Vector Hm north 1cm HEM gt B a quot7 gth B 1 ff Forces on the magnetic poles E quot E Magnetic field Magnitude of B BiotSavart Law perpena ular t0 the plane lts magnitude is CD sin 01 Plane of C and D Point at which field E is in the direction is evaluated of V X f Unit Vector Velocity of the charged particle Moving Charges Moving charges are the source of the magnetic field Magnetic eld llllb lb me point of the mov1ng a wl 7V 39 point charge HO qv Sln 6 to 11nd u B 4 direction of righthand rule 7 2 9 Velocity of the charged particle Field location Field strength T Surface of the earth 5 X 10 5 Refrigerator magnet 5 X 10393 Laboratory magnet 01 to 1 Superconducting magnet 10 Field of a Moving Charge Into page Line of motion Question The positive charge is moving straight out of the page What is the magnetic eld at the position of the dot a Up b Down c Left d Right e Out of the page Physics 113 Dr Renat Letfullin 22 Example The Magnetic Field of an Electron An electron is moving to the right as shown in the diagram What is the direction of the electron s magnetic eld at the position indicated by the black dot Since the electron has a negative charge the direction of B should be Z 7gtltf which is out of the diagram Physics 113 Dr Renat Letfullin 23 Position 3 Position 2 liositign 1 B1 0 W quot r v a 1 A a lt 4 m1 M o L vr n M I quotr 7 y Hf kang H H g y J Elmf 391 M J J quotquot 77 2 o 77 1 MML L 7 Z i quin6 B110 BO10sin45 2 47 057X10 13 10x10 3 m2 10 x10 NAm 160x10 13 IQT Superposition Magnetic elds obey the principle of superposition The magnetic elds from a number of moving charges add vectorially to produce a net magnetic eld In particular the magnetic elds produced by individual electrons moving in a currentcarrying wire add to produce a magnetic eld that is characteristic of the net current Physics 113 Dr Renat Letfullin 25 Multiplying Vectors 21 Ax Aj Azk E BX By 32 Ejg AXBX AFB A53 2 A BCos6AB 7 M LIL iueLfCHL Am Physics 13 Magnetic Force Ampere s Experiment Like cun ents attract P3175105 13 E Magnetic Force Plzmr nl FandB 3w 7 quot quot 39 Jmsms ij L31 Magnetic Force on Moving Charges Concept ProperTies of The magneTic force 1 Only moving charges experience The magneTic force There is no magneTic force on a charge aT resT vO in a magneTic field 2 There is no magneTic force on a charge moving parallel oFOO or anTiparallel oc1800 To a magneTic field 3 When There is a magneTic force iT is perpendicular To boTh v and B 4 The force on a negaTive charge is in The direcTion opposfe To va 5 For a charge moving perpendicular To B oc900 The magniTude of The force is maximum FIquB Physics 113 Dr Renat Letfullin E F pointing into page 29 Direction of Magnetic Force on Moving Charges Velocity B Force out of page right out of page left out of page up out of page down Thumb Fingers zq x Right Hand Rule Physics 113 Dr Renat Letfullin Palm 30 Direction of Magnetic Force on Moving Charges Velocity B Force out of page right up out of page left down out of page up 1Up 2 Down 3 Right 4 Left 5Zero B Right Hand Rule Thumb v Fingers B palm F Physics 113 Dr Renat Letfullin 31 Direction of Magnetic Force on Moving Charges Velocity B Force outofpage ght up out of page left down 6ut c5f 5age up left out of page down right B Right Hand Rule Thumb v Fingers B palm F v Negative Charge has opposite F Physics 113 Dr Renat Letfullin 32 ACT Moving Charges The three charges below have equal charge and speed but are traveling in different directions in a uniform magnetic field 1 Which particle experiences the greatest magnetic force 2 The force on particle 3 is in the same direction as the force on particle 1 1 True 2 False B KO Thumb v fingers B palm F 9 A Into page r39 i ll Physics 113 Dr R nat Letfullin 33 Comparison Electric vs Magnetic Force Electric Magnetic Source Charges Moving Charges Act on Charges Moving Charges Magnitude F qE F q v B sin6 Direction of F Parallel to E Perpendicular to vB Physics 113 Dr Renat Letfullin 34 9271 When a charged particle moves through a magnetic eld the direction of the magnetic force on the particle at a certain point is A in the direction of the magnetic eld at that point B opposite to the direction of the magnetic eld at that point C perpendicular to the magnetic eld at that point D none of the above E The answer depends on the sign of the particle s electric charge 9271 When a charged particle moves through a magnetic eld the direction of the magnetic force on the particle at a certain point is A in the direction of the magnetic eld at that point B opposite to the direction of the magnetic eld at that point J C perpendicular to the magnetic eld at that point D none of the above E The answer depends on the sign of the particle s electric charge 9271 A particle with a positive charge moves in the x2 plane as shown The magnetic eld is in the positive z direction The magnetic force on the particle is in A the positive xdirection B the negative xdirection C the positive ydirection D the negative ydirection E none of these 9271 A particle with a positive charge moves in the x2 plane as shown The magnetic eld is in the positive z direction The magnetic force on the particle is in A the positive xdirection B the negative xdirection C the positive ydirection J D the negative ydirection E none of these Movie Magnetism Part II
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