Physics II chapter 27 notes

Physics II chapter 27 notes - Chapter 27: Magnetic Field...

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V6.01 BPQ/RS F’10 76 Chapter 27: Magnetic Field and Magnetic Forces Moving (or “spinning”) charges cause axial- vector field called Magnetic Field, In this chapter… B Magnetic Field exerts a force on moving (or “spinning”) charges repulsive and attractive forces between objects known as magnets introduction to magnetic fields magnetic fields exert forces on moving electric charges & electric currents sources of magnetic fields to be studied in next chapter magnetic phenomena observed over 2500 years ago in Magnesia (Asia Minor) Magnetism (27-1) ‘loadstone’, ‘magnetite’ occur naturally as iron-containing minerals almost everything has some (weak) magnetic interactions strongly magnetic materials (eg Iron) have un-paired electrons orbiting (or “spinning”) which act like continuously moving charges. These can generate magnetic fields (permanent magnets) and ‘feel’ magnetic forces nickel, cobalt are strongly magnetic in the same way as iron is later study ‘paramagnetism’, ‘diamagnetism’, ‘anti-ferromagnetism’ before relationship of magnetic interactions to moving charges was understood, magnetic forces were described in terms of magnetic poles north and south poles (Historical names based on use as compass. .. north pole points North.) opposite poles attract, like poles repel (analogous to electric charges) S N S S N S N N
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V6.01 BPQ/RS F’10 77 BUT isolated electric charges exist, but a single isolated magnetic pole has “never” been observed poles always occur in north- south pairs; no “monopoles” the Earth itself is a magnet north pole of a compass needle points towards the geographical north pole this means magnetic south pole is close to Earth’s geographical north pole at Pittsburgh, compass needle dips about 68 o below horizontal magnetic pole continually drifts (average position moves 10-40 km each year; currently in Canada, eh?) fluctuates by up to 80 km in any given day! Earth’s magnetic poles flip every 250,000 years on average (last flip was 780,000 years ago!); the flip takes about 1000 years Earth’s magnetic field strength has decreased 10% in last 150 years similar to electric interactions, we describe magnetic interactions by saying that a bar magnet sets up a magnetic field in the space around it a uniform magnetic field exerts torques (not forces) on other bar magnets S N N Break apart S N S N S Break apart N S N YES! NO!
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V6.01 BPQ/RS F’10 78 magnetic field Magnetic Field and Magnetic Flux (27-3) () Br is an axial vector field (more on this later) direction of B is defined as the direction that compass needles point: So field lines outside a bar magnet run toward south pole of magnet and away from north pole .
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Physics II chapter 27 notes - Chapter 27: Magnetic Field...

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