Physics II - Lecture 5 (Magnetic Forces)

Physics II - Lecture 5 (Magnetic Forces) - Physics 1200...

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Physics 1200 Lecture 5 Magnetic forces Creating magnetic fields 1 Physics 2 - Persans - S2011
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Some observations • Certain chunks of metal exert force on one another even in the absence of net charge. • These chunks align with respect to each other. • We will associate the force with a new field – the magnetic field. • Similar forces are observed when charges move (current). • Magnetic fields are observed as dipole fields. Physics 2 - Persans - S2011 2
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In analogy with the electric field lines we introduce the concept of magnetic field lines which help visualize the magnetic field vector without using equations. The relation b B Magnetic Field Lines : etween the magnetic field lines and are: B 1. At any point P the magnetic field vector B is tangent to the magnetic field lines P P B magnetic field line 2. The magnitude of the magnetic field vector B is proportional to the density of the magnetic field lines magnetic field lines P Q P B Q B PQ BB 3 Physics 2 - Persans - S2011
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The magnetic field lines of a permanent magnet are shown in the figure. The lines pass through the body of the magnet and form loops. This is in contr Magnetic field lines of a permanent magn d et close ast to the electric field lines that originate and terminate on elecric charges. The closed magnetic field lines enter one point of the magnet and exit at the other end. The end of the magnet from which the lines emerge is known as the of the magnet. The other end where the lines enter is called the of the magnet. The two poles of the magnet cannot be separated. Together they north pole south pole form what is known as a " " magnetic dipole 4 Physics 2 - Persans - S2011
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Physics 2 - Persans - S2011 5 Magnetic Force on a Moving Charge B v q F q: charge of the particle (C; + or –) v : velocity of the particle (m/s) B : magnetic field (T) Force is at a right angle to velocity. Force is at a right angle to magnetic field. Important: If q is negative, that reverses the direction of force.
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Physics 2 - Persans - S2011 6 Vector Cross Product b a c ; ) sin( | b | | a | | c | The direction comes from the right-hand rule. It is at a right angle to the plane formed by a and b . In other words, the cross product is at right angles to both a and b . (3D thinking required!) a b c a b 
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Physics 2 - Persans - S2011 7 The vector components of vector are given by the equations: , ˆ ˆ ˆ ˆ ˆ ˆ ˆ ˆ ˆ , , x y z z y x y z x y z x y z c a b a b a a i a j a k b b i b j b k c c i c j c k c  c = a×b The Vector Product in terms of Vector Components Those familiar with the use of determinants can use the expression cc , y z x x z z
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This note was uploaded on 03/21/2011 for the course PHYS 1200 taught by Professor Stoler during the Spring '06 term at Rensselaer Polytechnic Institute.

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Physics II - Lecture 5 (Magnetic Forces) - Physics 1200...

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