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Unformatted text preview: Chapter 21 Magnetic Forces and Magnetic Fields 21.1 Magnetic Fields The needle of a compass is permanent magnet that has a north magnetic pole (N) at one end and a south magnetic pole (S) at the other. 21.1 Magnetic Fields The behavior of magnetic poles is similar to that of like and unlike electric charges. 21.1 Magnetic Fields Surrounding a magnet there is a magnetic field . The direction of the magnetic field at any point in space is the direction indicated by the north pole of a small compass needle placed at that point. 21.1 Magnetic Fields The magnetic field lines and pattern of iron filings in the vicinity of a bar magnet and the magnetic field lines in the gap of a horseshoe magnet. 21.1 Magnetic Fields 21.2 The Force That a Magnetic Field Exerts on a Charge When a charge is placed in an electric field, it experiences a force, according to E F q = 21.2 The Force That a Magnetic Field Exerts on a Charge The following conditions must be met for a charge to experience a magnetic force when placed in a magnetic field: 1. The charge must be moving. 2. The velocity of the charge must have a component that is perpendicular to the direction of the magnetic field. 21.2 The Force That a Magnetic Field Exerts on a Charge Right Hand Rule No. 1. Extend the right hand so the fingers point along the direction of the magnetic field and the thumb points along the velocity of the charge. The palm of the hand then faces in the direction of the magnetic force that acts on a positive charge. If the moving charge is negative, the direction of the force is opposite to that predicted by RHR1. 21.2 The Force That a Magnetic Field Exerts on a Charge DEFINITION OF THE MAGNETIC FIELD The magnitude of the magnetic field at any point in space is defined as ( 29 θ sin v q F B o = where the angle (0<θ<180 o ) is the angle between the velocity of the charge and the direction of the magnetic field. SI Unit of Magnetic Field: ( 29 T tesla 1 meter coulomb second newton = ⋅ ⋅ tesla 10 gauss 1 4 = 21.2 The Force That a Magnetic Field Exerts on a Charge Example 1 Magnetic Forces on Charged Particles A proton in a particle accelerator has a speed of 5.0x10 6 m/s. The proton encounters a magnetic field whose magnitude is 0.40 T and whose direction makes and angle of 30.0 degrees with respect to the proton’s velocity (see part (c) of the figure). Find (a) the magnitude and direction of the...
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This note was uploaded on 02/20/2010 for the course PHYSC 210 taught by Professor Uscinski during the Summer '09 term at American.
 Summer '09
 Uscinski

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