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motor effect
when a current-carrying wire is placed in a magnetic field, the magnetic interaction between the conventional current and magnetic field results in a force.
F = BIL sin theta
sin theta is between B and I → max force at 90, no force at 0 (parallel)
units of B is tesla
tesla
the magnetic flux density of 1 tesla will cause a wire of length 1m carrying current of 1A that is perpendicular to the field to experience a force of 1N
magnetic field due to current carrying wire
parallel current-carrying conductors
the current in each wire produces a magnetic field, the other wire is in the field so it experiences a force.
force per unit length calculated using Ampere’s force law: F/L
direction of magnetic field at any point is the tangent to the circular field.
magnetic field is out of paper
even though current rotates, angle between B and I is still perpendicular → sin theta same, magnitude of F same
charges in magnetic fields on a microscopic level
each electron in the wire experiences force as it travels through magnetic field → note electron flow is opposite to conventional current
sum of forces causes total force on wire F = BIL
if per electron, F=Bqv
motion of charged particle in magnetic field
F=qvBsintheta, if theta (angle between B and I) = 90, undergoes circular motion
magnitude of v unchanged but direction changes by FLHR
F provides centripetal force, work done = 0 since v is perpendicular to F at all times
magnetic force = centripetal force → r = mv sintheta/qB
if charged particle moves through magnetic field at an angle, experiences helical motion
perpendicular component vsintheta causes circular motion
parallel component vcostheta is uniform
motion of charged particle in crossed electric/magnetic fields
parabolic motion
Fb and Fe balanced, Bqv = qE → v=E/B
F not perpendicular to v! just downwards all the time
condition for charged particle to experience force in a magnetic field
velocity of charged particle must have a component perpendicular to the direction of the magnetic field