Magnetic fields And Forces

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magnetic fields and forcesphysics 112N

bar magnet & iron filingsphysics 112N2

bar magnetsphysics 112N3

the Earth’s magnetic fieldphysics 112N4

‘electro’-magnetism! is there a connection between electricityand magnetism ?! place a compass near a current carryingwirephysics 112N5

‘electro’-magnetism! is there a connection between electricity and magnetism ?! a loop carrying a large currentphysics 112N6

magnetic fields! a vector at each point in space! compasses line up along thesevectors! will produce a force on anymoving charge (more later)physics 112N7

magnetic fields! a vector at each point in space! compasses line up along thesevectors! will produce a force on anymoving charge (more later)physics 112N8

magnetic fieldsphysics 112N9

magnetic fields! a vector at each point in space! compasses line up along thesevectors! will produce a force on anymoving charge (more later)physics 112N10

magnetic fieldsphysics 112N11

magnetic fieldsphysics 112N12

magnetic field superposition! just as the total electric field at any point is the vector sumof the fields from all charges nearby,! so the total magnetic field is the vector sum of the fieldsfrom all magnetic sources nearby.! Consider two solenoids producing nearly uniform fields:physics 112N13

magnetic field superpositionphysics 112N16

magnetic forces! magnetic fields produce a force on chargedparticles that are moving through them! experiments show that the strength of theforce is proportional to· the charge· the speed of the particle· the magnitude of the magnetic field! experiments also show the direction theforce acts in· perpendicular to the velocity· perpendicular to the magnetic fieldphysics 112N17

magnetic forces - the right-hand rulephysics 112N18

magnetic forces - the right-hand rulephysics 112N19

proton beam through a magnetic fieldA beam of protons moves through a uniform magnetic field withmagnitude 2.0 T, directed along the positive z-axis. The protonshave a velocity of magnitude 3.0x105 m/s in the xz-plane at anangle of 30o to the positive z-axis. Find the magnitude anddirection of force on the proton.physics 112N21

motion of charged particles in a magnetic fieldconsider a positive charge moving in a planeperpendicular to a uniform magnetic fieldforce is always perpendicular to the velocityand is of constant magnitudeconstant acceleration perpendicular to thevelocity circular motionradius of the circle determined byphysics 112N25

protons in a magnetic fieldA beam of protons traveling at 1.20 km/s enters auniform magnetic field traveling perpendicular to thefield. The beam exits the magnetic field in a directionperpendicular to its original direction. The beam travels adistance of 1.18 cm in the field. What is the magnitude ofthe magnetic field ?physics 112Nprotonpath27

force on a current carrying conductor! what happens if we put a wire carrying current into a magnetic field?! it contains moving charges, so we’d guess it feels a forcewe can work out a formula for the force:force on each chargein time Δt, a charge Q I Δt flows inin time Δt, a charge movesso the total charge in the rod isthe total force on the rod isphysics 112N28

force on a current carrying conductor! if the magnetic field is not perpendicular to the wire, then the formula is modified! only the perpendicular component of the B-field contributes to the forcephysics 112N29

force and torque on a current loop! what happens if we put a closed current loop into a magnetic field?e.g. consider a rectangular current carrying loop of wire in a uniform fieldphysics 112N31

force and torque on a current loop! what happens if we put a closed current loop into a magnetic field?e.g. consider a rectangular current carrying loop of wire in a uniform fieldzxphysics 112N32

force and torque on a current loop! what happens if we put a closed current loop into a magnetic field?e.g. consider a rectangular current carrying loop of wire in a uniform fieldzxloop feels a torquephysics 112N33

force and torque on a current loop! what happens if we put a closed current loop into a magnetic field?e.g. consider a rectangular current carrying loop of wire in a uniform fieldzxphysics 112N34

force and torque on a current loop! what happens if we put a closed current loop into a magnetic field?e.g. consider a rectangular current carrying loop of wire in a uniform fieldzxphysics 112N35

force and torque on a current loop! what happens if we put a closed current loop into a magnetic field?e.g. consider a rectangular current carrying loop of wire in a uniform fieldN.B. the animation isn’t showing the actual motioncaused by the torque, just the variation of force with anglephysics 112N36

solenoid in a uniform field! the torque on the solenoid tends to line itup along the field! same thing that a bar magnet doesphysics 112N40

magnetic field from a long straight wireWe now know what happens to moving charges and current carryingwires in magnetic fields! but how do we generate a magnetic field?! turns out we can generate magnetic fields using electrical currents! simplest example is a long, straight current-carrying wiremagnitude of field aperpendicular distance rfrom a wire carryingcurrent Ipermeability of vacuumμ0 4!"10-7 Tm/A(magnetic analogue of ε0)physics 112N41

magnetic field from a long straight wirephysics 112N42

solenoidfield strength inside the coiln turns per unit lengthphysics 112N45

typical field strengthstypical field strength from a wire1 cm away from a wire carrying 10 A,B 10-4 T 1 Gausstypical field strength in a solenoid200 turns in 10cm length carrying 10 AB 10-2 T 10 Gaussa strong fridge magnetclose to the pole,B 10-1 T 100 GaussEarth’s magnetic fieldB 5!10-5 T 0.5 Gausselectromagnet with an iron coreB 1 T 104 Gausssuperconducting electromagnets (e.g. in the LHC)B 10 T 105 Gaussphysics 112N47

n turns per unit length. physics 112N 47 typical field strengths typical field strength from a wire Earth’s magnetic field typical field strength in a solenoid a strong fridge magnet electromagnet with an iron core superconducting electromagnets (e.g. in the LHC)

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