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**Unformatted text preview: **Class 10 Magnetic Forces Physics 106 Fall 2011 Press CTRL-L to view as a slide show. Learning Outcomes Las time we learned about: I Examples of Series-Parallel Reduction I Series RC Circuits and Time Constants I Using Kirchhoff’s Rules I The Origin of Magnetic Fields I The Lorentz Force Learning Outcomes Today we will discuss: I Examples of the Lorentz force. I Magnetic forces on a wire. I Motion of a charge in a magnetic field. I Torques and forces on current loops. I Electric Motors Examples of the Lorentz Force The Magnetic Force I Call the angle between the vectors θ I The magnitude of the force is F = qvB sin θ The Magnetic Force I The force is perpendicular to ~ v and to ~ B and is given by the "right-hand rule." Right Hand Rule #1 I Place your fingers in the direction of ~ v . I Curl your fingers into the direction of the magnetic field, ~ B . I Your thumb points in the direction of the force, ~ F , on a positive charge I If the charge is negative, the force is opposite that determined by the right hand rule. Velocity Selector Positive ions travel undeflected through a region containing both electric and magnetic fields. If E = 1000 V/m and B = 0.100 T, how fast are the ions moving? F E = qE = qvB sin θ 90 ◦ = F B v = E B = 1000 . 100 m / s = 10000 m / s Magnetic Forces on a Wire Magnetic Force on a Current-Carrying Wire I A force is exerted on a current-carrying wire placed in a magnetic field I The current is a collection of many charged particles in motion I The direction of the force is given by right hand rule #1 Force on a Wire I The magnetic force is exerted on each moving charge in the wire I The total force is the sum of all the magnetic forces on all the individual charges producing the current I F = BI ‘ sin θ I θ is the angle between ~ B and the direction of I I The direction is found by right hand rule #1, placing your fingers in the direction of I instead of ~ v Force on a Wire I The blue × indicate the magnetic field is directed intothe page I The × represents the tail of an arrow I Blue dots ◦ would be used to represent a field directed out of the page I The ◦ represents the head of an arrow I In this case, there is no current, so there is no force Force on a Wire I ~ B is into the page I The current is up I The force is to the left Force on a Wire I ~ B is into the page I The current is down I The force is to the right Motion of a Charged Particle in a Magnetic Field Force on a Charged Particle in a Magnetic Field...

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