# Magnets and the magnetic field Electric currents create magnetic fields

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Chapter 24 Magnetic Fields and Forces. Topics:. Magnets and the magnetic field Electric currents create magnetic fields Magnetic fields of wires, loops, and solenoids Magnetic forces on charges and currents Magnets and magnetic materials. Sample question:. - PowerPoint PPT Presentation

### Text of Magnets and the magnetic field Electric currents create magnetic fields

• Magnets and the magnetic fieldElectric currents create magnetic fieldsMagnetic fields of wires, loops, and solenoids Magnetic forces on charges and currentsMagnets and magnetic materialsChapter 24Magnetic Fields and ForcesTopics:Sample question:This image of a patients knee was made with magnetic fields, not x rays. How can we use magnetic fields to visualize the inside of the body?Slide 24-1

• Key PointsThree types of magnetic interactionsno interaction with either pole of a magnet => object is non-magneticattracted to both poles of a magnet => object is magneticAttracted to one pole and repelled by the other pole => object is a magnetMagnetic field vector from a bar magnet is a super position of the magnetic field vectors from the N and S poles:Vector from N pole points away from N pole Vector from S pole points towards S poleField lines form complete loops inside and outside of magnetField lines outside magnet go from N to S polesField lines inside magnet go from S to N polesMagnetic Field vectors at a point are tangential to Magnetic Field Lines

• 3-D Arrows, Cross Products, and Right Hand Rule 1Slide 24-2Showing vectors in 3D

Cross Product

For direction use Right-hand rule 1

Right-hand rule 1 (RHR 1) => for finding direction of cross-product vector (Cross-Product Rule)Point right hand in the direction of the first vector (vector A)Rotate your right hand until you can point your fingers in the direction of the second vector (vector B)Thumb points in direction the cross-product vector (vector C)

• Right Hand Rules for MagnetismRight-hand rule 1 (RHR 1) => for finding magnetic force FB= q*v_vector x B_vector (Cross-Product Rule)Point right hand in the direction the charges are moving (current or velocity)Rotate your right hand until you can point your fingers in the direction of the magnetic FieldThumb points in direction of force for + charge Force is in opposite direction for - charges

Right-hand rule 2 (RHR 2) => Finding direction of B from IPoint thumb of right hand in direction of current I, B-field lines curl in direction of fingers

Right-hand rule 3 (RHR 3) => Finding direction of current in a loop from direction of B-fieldPoint thumb of right hand in direction of B-fieldFingers of right hand curl in direction of currentSlide 24-2

• Drawing Field Lines of a Bar MagnetSlide 24-10

• Magnetic Fields Produced by Bar MagnetsA single bar magnetA single bar magnet(closeup)Slide 24-11

• Magnetic Fields Produced by Bar MagnetsTwo bar magnets, unlike poles facingTwo bar magnets,like poles facingSlide 24-12

• Magnetic Fields from Two MagnetsBar Magnets A and B are placed at right angles. Two compasses, X and Y are placed so that they are equidistant from the two magnets as shownA.) The arrow in compass X indicates the direction in which the North pole of the compass is pointing. Indicate the North and South ends of both magnets in the diagram

B.) Draw an arrow in compass Y to show the direction in which the North pole of the compass needle would point.

Slide 24-2

• Electric Currents Also Create Magnetic FieldsA long, straight wireA current loopA solenoidSlide 24-15

• The Magnetic Field of a Straight Current-Carrying WireSlide 24-16

• Slide 24-17

• Representing Vectors and Currents That Are Perpendicular to the PageSlide 24-18

• Checking UnderstandingPoint P is 5 cm above the wire as you look straight down at it. In which direction is the magnetic field at P?Slide 24-19

• AnswerPoint P is 5 cm above the wire as you look straight down at it. In which direction is the magnetic field at P?Slide 24-20

• Drawing Field Vectors and Field Lines of a Current-Carrying WireSlide 24-21

• Drawing a Current LoopSlide 24-22

• The Magnetic Field of a Current LoopSlide 24-23

• The Magnetic Field of a SolenoidA short solenoidA long solenoidSlide 24-24

• The Magnitude of the Field due to a Long, Straight, Current-Carrying WireSlide 24-25

• Slide 24-26

• Checking Understanding10 A to the right.5 A to the right.2.5 A to the right. 10 A to the left.5 A to the left.2.5 A to the left.The magnetic field at point P is zero. What are the magnitude and direction of the current in the lower wire? Slide 24-27

• 5 A to the left.The magnetic field at point P is zero. What are the magnitude and direction of the current in the lower wire? Slide 24-28Answer

• The Magnetic Field of a Current LoopSlide 24-29

• ExampleWhat is the direction and magnitude of the magnetic field at point P, at the center of the loop?Slide 24-30

• The Magnetic Field Inside a SolenoidMagnetic field inside a solenoid of length L with N turns.Slide 24-31

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