Phys - Magnetic Fields & Induction Flashcards
(15 cards)
Describe Hall Voltage
As electrons pass through a conductor with an external magnetic field acting on it, they accumulate on one side of the conductor in response to the magnetic force.
This causes an increasing electric field to be generated due to the increasing charge difference between two sides of the conductor.
Once electrons are no longer deflected, the field forces are balanced.
The potential difference between the conductor sides that this occurs at is the Hall Voltage.
Determining Hall Voltage
F = Bqv
F = Eq
E = Vh / d
Bvd = Vh
Fleming’s LHR
Current represents the motion of a positively charged particle (velocity parallel)
Describe Faraday’s Law
When magnetic field lines are cut, flux is changing. Due to Faraday’s Law, emf is directly proportional to the negative rate of change of flux linkage wrt time, so electromotive force is induced.
Magnet Dropped Vertically Into Coil / Describe Emf Induced
Initially, emf will increase as the magnet approaches the coil since field lines are being cut. Just before the center is reached, a peak emf is induced, which quickly reduces to 0 when there is no change in flux while the magnet is in the center, as approaching cut fields are being cancelled by those leaving the coil.
Now, flux decreases from the maximum as the magnet leaves the coil, inducing an emf in the opposite direction of the initial one.
second peak is greater due to gravitational acceleration
Magnet Dropped Vertically Into Coil / Describe Forces
As the magnet is moving into the coil, a field which opposes its motion is induced, inducing a Lorentz force which points upwards. Same for leaving the coil. Matches the peaks of induced emf.
This decreases to 0 when there is no current induced in the coil while in the center.
Linear Accelerator
Drift tubes are placed in a straight line.
Particles are accelerated using electric fields between tubes, which alternate whenever the particle moves through it for continuous acceleration.
Frequency of alternation is kept constant, accounted for by the increasing length of drift tubes as the particle’s speed increases.
Used in medical radiation therapy
Cyclotron
Dees are placed next to each other with a gap in between.
An alternating electric field between the dees is used to accelerate the particles.
A magnetic field perpendicular to the dees combined with the increasing speed causes particles to move in circular motion with increasing radius.
Used in radioactive isotope production
Synchrotron
A circular ring with gaps distributed along it.
Alternating electric fields are used to accelerate particles.
A perpendicular magnetic field with increasing field strength is applied to the ring to keep the accelerating particles in circular motion with constant radius.
Alternating frequency must increase to match the particle’s speed.
Used in high-energy physics research
How Is RMS Related To Peak?
Vrms = sqrt(Vpeak^2 / 2)
Fleming’s RHR
FORCE - opposite direction of change that induced emf
FIELD - direction of initial magnetic field
CURRENT - direction of current flow due to induced emf
Only works for linear conductors
Fleming’s Right Hand Grip Rule
THUMB - current direction
FINGERS - field direction
for linear conductors
OR
THUMB - induced field direction
FINGERS - current direction
for circular conductors
Field Line Direction
N to S
Current Carrier In External Field / Describe Forces
Force felt by the magnet due to Fleming’s LHR in some direction
Opposite force felt by the carrier by N3L
Why Are Log Graphs Better?
Data points are spread out, in regular graphs they tend to be bunched together
