Electromagnetism Flashcards
what can magnetic field between to very close magnets be approximated to
uniform
what can the field inside a solenoid be approximated to
uniform
definition of magnetic flux density
number of magnetic flux lines through a region of space per unit area (measure of strength of the magnetic field)
what is the definition of 1 tesla
flux density that causes a force of 1 N on a 1m wire carrying a current on 1 amp at right angles to the flux (think of f=BIL equation)
how do you derive the equation F=BQv
sub in I=Q/t into F=BIL
how to find the radius of the arc of a free moving charge in a magnetic field
Mv^2/r = BQv
where are cyclotrons used
in particle accelerators to create a high energy beam of electrons
what is a cyclotron
2 semicircular D’s with perpendicular to a strong uniform magnetic field with an alternating electric b field between the D’s
how is a particle accelerated by a cyclotron
particles accelerates to opposite charged end of electric field
it is then turned in a semicircle by a centripetal magnetic force as it enters the D
Alternating P.D has switched therefore switching the direction of the electric field accelerating the particle through it again in the other direction.
radius of particles trajectory gets bigger as r∝v therefore causing the electron to leave cyclotron with high velocity
what is the energy a charged particle gains as it travells across a P.D
E = QV
what is electromagnetic induction
An EMF is induced when there is relative movement between a conductor and a magnetic field
what is Faradays law
induced EMF is directly proportional to the rate of change of magnetic flux
what is lenzs law
the direction of the induced EMF is such as to oppose the change inducing it
what is the equation for the EMF induced by a straight conductor in a uniform magnetic field
EMF = BLv
how can you induce a higher EMF when moving a bar magnet in and out of a conducting coil
more coils
high speed when moving bar magnet
increase strength of magnet
how does a transformer work
AC in primary coil creates a changing magnetic solenoid through the coil. The field is around the soft iron core to the secondary coil where because the direction of the field is changing it induces a EMF in the wires of the secondary coil
What remains the same between the P.D of primary and secondary AC
frequency of AC
why is a soft iron core used
directs magnetic field and is easily demagnitised and magnitised
sources of inefficiancy in a transformer
eddy currents
heat in wires
how to reduce inefficiency in transformers
high resistivity of core
laminating core
thick wires
what are eddy currents
current is induced in the iron core because it is conductive therefore the electric energy is dissipated as heat to the wires reducing efficiency of transformer
