General Physics 2Magnetism1 Mass Spectrometer Used to identify atoms and their concentrations in a sample of material. Between S1 and S2, molecules go straight if q E = q v B or v = E/B After S2, B produces circular motion q v B’ = m v 2 /r m = q B’ r/v = q B B’ r/E Found isotopes

General Physics 2Magnetism2 E8 – Topics to cover Magnetic Force on a wire Torque on a wire Electric Motors - lab Creating currents in moving loops Eddy currents in moving conductors

General Physics 2Magnetism3 Force on a wire Magnetic force of a straight wire segment

General Physics 2Magnetism4 Demo: Magnetic Force Interaction between B field and current Moving charges are affected by B fields

General Physics 2Magnetism5 Force on Current in B Field Direction of F given by Right Hand Rule fingers = I bend fingers = B thumb = F (for uniform field)

General Physics 2Magnetism6 Think-Pair-Share (a) What is the magnitude of the force per meter of length on a straight wire carrying an 8.40-A current when perpendicular to a T uniform magnetic field? (b) What if the angle between the wire and field is ?

General Physics 2Magnetism7 Torque on a wire A loop carrying a current will experience a torque which causes the loop to ROTATE! μ is the loop’s magnetic moment Expresses the strength and south-to-north orientation of the loop’s equivalent bar magnet

General Physics 2 Magnetism 8 Torque on a Loop Forces on segments of a loop cause the loop to rotate Simplify by replacing loop with magnet Fingers in direction of current, thumb represents NORTH pole of magnet Think about the loop as a magnet will rotate so that the north face of the magnet points in the direction of the magnetic field

General Physics 2 Magnetism 9 Electric Motors - Torque In each orientation, which way will the loop rotate? Changing the direction of the current will keep the loop spinning

Commutator To change the direction of the current and keep the loop spinning, a commutator is used General Physics 2Magnetism10

General Physics 2 Magnetism 11 Eddy currents in moving conductors You can create a current in a metal plate by moving the plate through a magnetic field. Current density will be constant in the region of the magnetic field

General Physics 2Magnetism12 Practice Problems Magnetism: Worksheets 3 and 5 Finish before next class

Group Problems E8B.1 E8B.4 E8S.5 General Physics 2Magnetism13