Physics Quiz 6

  • Magnet: 2 poles, North and South

  • Needle is permanent magnet

  • Magnetic field (B) surrounds a magnet

  • Magnetic field lines: out from N to S

  • Direction of field vector is tangent, # lines is proportional to magnetic field, form closed loops

  • RHR: curl fingers from v to b, thumb is direction of positive charge

  • For charge to experience magnetic force in field

    • Moving 

    • Velocity perpendicular to magnetic field

    • Magnetic force perpendicular to VB plane

  • Magnetic field units: Tesla, gauss  = 10^-4 T

  • Charged particle in electric field: F acts on charge parallel to E, trajectory bends in horizontal plane

  • Charged particle in magnetic field: F acts on charge perpendicular to B, trajectory bends in vertical plane 

  • To balance electric and magnetic force, set them equal, v = E/B

  • Electrical field CAN do work on particle

  • Magnetic field CANNOT do work on particle- cos 90 = 0 (perpendicular to particle motion)

  • For circular force, use centripetal force, set equal to magnetic

  • Mass spec: measure mass + abundance of isotopes (same protons, different neutrons)

  • Magnet force: charged particle in magnetic field

    • Can also be on current 

    • RHR to find force direction on wire

    • F = ILBsintheta

  • MHD propulsion: water expelled from rear so boat moves forward (3rd law)

  • Right hand rule for current: thumb is I, half circle fingers point in B direction 

  • Long wire to avoid fringe field effects

  • Wires in opposite directions repulse

  • Wires in same direction attract

  • Find B field at center in loop

  • Solenoid: made of many current loops, characterized by number of turns per length (n), use RHR for direction inside 

    • Find L of solenoid by doing 2pir* turns

  • Loop in magnetic field: equal magnitude but opposite direction, loop rotates so normal force aligned with magnetic field 

  • Galvanometer: coil rotates when there is a current, stops when torque on coil canceled by torque on spring

  • DC motor: separated so left is up, right is down

    • When current exists, experiences a torque

    • Continues to rotate bc of inertia when no current