chapter27--PHY 131 JAB

# chapter27--PHY 131 JAB - 1 Chapter 27 Magnetic field and...

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Unformatted text preview: 1 Chapter 27: Magnetic field and magnetic forces 2 All magnets have at least one north pole and one south pole. Field lines emerge from north poles and enter through south poles. §27.1- 27.2 Magnetism and magnetic fields Magnetic Dipole 3 Magnets exert forces on one another. Opposite magnetic poles attract and like magnetic poles repel. Magnetic fields arise from 1. Moving electric charges 2. Some particles have an intrinsic magnetic field 4 Magnetic field lines are closed loops. There is no (known!) source of magnetic field lines. (No magnetic monopoles.) If a magnet is broken in half you just end up with two magnets. 5 Near the surface of the Earth, the magnetic field is that of a dipole. Note the orientation of the magnetic poles! 6 Away from the Earth, the magnetic field is distorted by the solar wind. 7 Evidence for magnetic pole reversals has been found on the ocean floor. The iron bearing minerals in the rock contain a record of the Earth’s magnetic field. 8 Consider a region of space that has a magnetic field B . Experiments show that 1. The magnetic force on a particle is proportional to the particle’s charge 2. The magnetic force on a particle is proportional to the particle’s velocity 3. The magnetic force is perpendicular to both the magnetic field and the particle’s velocity. 9 ( ) B v F × = q B The unit of magnetic field ( B ) is the tesla (1T = 1 N/Am). Note: 1 Gauss (G) = 10-4 T. Summarizing the experiments mathematically: 10 The magnitude of F B is: ( ) θ sin B v qB F = Where vsin θ is the component of the velocity perpendicular to the direction of the magnetic field. θ represents the angle between v and B . θ v B Draw the vectors tail- to-tail to determine θ . 11 Example: An electron moves with speed 2.0 × 10 5 m/s in a 1.2 Tesla uniform magnetic field. At one instant, the electron is moving due west and experiences an upward magnetic force of 3.2 × 10-14 N. What is the direction of the magnetic field?...
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chapter27--PHY 131 JAB - 1 Chapter 27 Magnetic field and...

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