PPE33_MovingCharges

# PPE33_MovingCharges - Magnetism Moving Charges I RHJansen...

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© RHJansen Magnetism Magnetism Moving Charges I Moving Charges I

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© RHJansen Force of Magnetism on Moving Charges A moving charge is a tiny magnet. If a moving charge moves through an external magnetic field (the field due to another magnetic), then the two magnets will interact. There will be an equal an opposite force on the charge and the external magnet. However, the charge is very small and the external magnet is very large. As a result, we will see the charge affected by the force while the same force creates negligible affects on the external magnet. The force of magnetism on a charge moving in a magnetic field is F B = qvB sin q F B Force of magnetism Newtons (N) q Charge (usually an electron or proton) Coulombs (C) v Velocity of the charge meters per second (m/s) B Magnetic field strength Tesla (T) sin θ Refers to the angle between the vectors v and B © RHJansen
Motion of Charges in Magnetic Fields. There will only be a force of magnetism if there are two magnets to push on each other. Start with a set of fixed magnets to create a uniform magnetic field. Examine how the field from the fixed magnets pushes (forces) a second magnet (charge) © RHJansen S N S N B + v + v = 0 + v + v + v Inertia F B = 0 F B = 0 F B = 0 F B = qvB F B = qvB sin q Inertia Inertia Circular Motion Spiral Formulas containing sin (cross product) involve perpendicular vectors. Force only occurs if there is a component of velocity perpendicular to the magnetic field. If we know that sin θ is telling us to use the perpendicular component (and we know how to find it) then we can leave sin θ out of the equation. Inertia: the object will continue doing what it is doing.

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Comparing Electric and Magnetic Fields Let’s see how these same charges would be affected by an electric field. © RHJansen S N S N B + v + v = 0 + v + v + v Inertia Inertia Inertia Circular Motion Spiral + + + + + + E + v + v = 0 + v + v + v Speed up right Speed up right Slows left, Stops, Speeds up right Projectile Projectile
© RHJansen Circular Motion If a charge is moving perpendicular to magnetic field then the resulting motion will be uniform circular motion. Sum all the forces

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## This note was uploaded on 07/21/2009 for the course PHYSICS 7B taught by Professor Packard during the Spring '08 term at Berkeley.

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PPE33_MovingCharges - Magnetism Moving Charges I RHJansen...

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