Magnetism
- Magnets
- Experiment:
- suspend magnet
- mark end pointing north - N (pole)
- mark end pointing south - S (pole)
- repeat for second magnet
- Observation:
- North poles repel.
- North and south attract.
- South poles repel.
- Magnetic Field
- Field surrounds magnetic material
- magnetic force
- described in terms of field
- Direction
- determined by compass needle
- lines up with field.
- Experiment (only magnetic field present)
- project moving charge through a point
- charge experiences force
- force is always at a right angle to v
- size of force changes with direction of v
- zero in one direction, max 90o from that direction
- varies as the sine of the angle
- force changes as speed of charge changes
- charge experiences force
- size of force depends on size of charge
- direction of force changes direction when q changes sign
- Use to define magnetic field
- B used to represent magnetic field
- B = F/qv sinq
- Measuring B (two separate measurements)
- find direction of v in which a charge experiences no force.
- parallel to magnetic field
- with v perpendicular to this direction
- measure F
B = F/qv
- B measured in [N-s/C-m] = Tesla = T
- The force on a moving charged particle
- According to the rules for a cross product, the magnitude of F is given by
- the direction of the force is perpendicular to both B and v and can be determined by the right hand
rule
- To find directions: "Right hand rule"
- thumb - velocity
- fingers - magnetic field
- palm - force
- Conditions for non-zero work
- force
- displacement parallel to force
- Magnetic Force
- always perpendicular to velocity
- always perpendicular to displacement
- NO WORK DONE by Magnetic Force!
- Magnetic vs. Electric Field
- Similarities
- both represented by field lines
- strength proportional to # of lines
- Differences
- electric field lines begin and end on charges
- magnetic field lines form loops
- Examples
