Magnetic fields (unit 4) Flashcards
Number of times proton moves between a gap in a cyclotron?
ev divided by pd
How to work out where the force acts ON the wire?
-Fleming’s left hand rule
How to work out force acting on the current carrying wire?
-BIL sin theta
How to work out force for individually charged particles?
-BQV sin theta
Unit for magnetic field?
-Tesla (T)
How does Hall Voltage work?
-When a current flows at 90° through a magnetic field, there
will be a force on the electrons
-forcing them to one surface of the conductor.
-causing one surface to become negative and the other positive.
This creates an electrical field between the surfaces and cause
a force on the electrons in the opposite direction.
-the magnetic force and the electrical force will balance and an equilibrium is
reached.
-Hall voltage is the pd between surfaces at this equilibrium
How to work out Hall Voltage?
Hall Voltage =Bvd
What does the magnetic field look like in a straight wire?
- circles going around wire ( use right hand grip rule to determine direction of field)
What does the magnetic field look like in a solenoid?
- looks like a bar magnet (direction is the same as direction of current)
How to work out B in a wire?
- B = π µ 0 I/ 2 pi a
a is the distance from wire (radius for where you want field)
How to work out B in a solenoid?
-B = μo nI
n is number of turns per meter
n= number of turns/ length
How to increase field strength in a solenoid?
-adding an iron core
How do parallel current carrying wires exert a force on eachother?
- When a current passes through a wire it creates a magnetic field.
-the top wire will have a magnetic FIELD towards the bottom one (right hand grip rule)
-As current perpendicular to this field, due to LHR bottom wire there is a force on top wire from bottom
-due to Newton’s third law , there will be an equal force emitted by both wires on each other
What happens when putting a charged particle in a uniform magnetic field?
-Magnetic forces always act perpendicular to the motion. Therefore,
the magnetic force acts as a centripetal force and makes the charges
move in a circular path.
How to work out B field in uniform magnetic field?
BQV= mv^2/r
What happens when putting a charged particle in a uniform electric field?
-The electrical force between two parallel plates is constant due to the uniform electric field.
- the force acting on the electron here, will cause a vertical acceleration but not
change its horizontal velocity.
How do particle accelerators work?
-when the force and motion are in the same direction, the particle will gain kinetic energy as it is accelerated by the electric field
- use an alternating p.d. to accelerate the particles in the gaps between electrodes.
How to work out increase in KE in a particle accelerator?
-q x PD
How to work out acceleration in uniform electric field?
- F=ma
-qv/d = ma
Linear particle accelerator?
- path - straight line
- magnetic field - none
-alternating PD - Constant, increasing length of tube ensuresthe p.d. changes in time
Cyclotron particle accelerator?
- path - Circular but with increasing radius
-magnetic field - Constant, to ensure circular motion
-alternating PD - Constant, increasing path length ensures the p.d. changes
in time
Synchotron particle accelerator?
-path - Circular, constant radius
-magnetic field - Increasing to ensure circular motion with constant r
-alternating PD - Increasing
How to work out frequency for a CYCLOTRON and SYNCHOTRON?
F = BQ/2piM
How to derive equation for frequency for CYCLOTRON and SYNCHOTRON?
BQV= mv^2/r
v=ωr and ω=2πf
What direction does conventional current flow?
-opposite flow of electrons
INVESTIGATION OF MAGNETIC FLUX DENSITY USING A HALL PROBE practical ?
-Place the Hall probe into a known magnetic field, B1 and note the Hall potential difference, V1
-Then place the Hall probe in the centre of a solenoid
-Ensure, in both cases, the probe is at 90o to the magnetic field
- Again measure the Hall potential difference, V2 when the probe
is in the solenoid
The unknown magnetic field of the solenoid, B2, can be found using
𝐵2 =(B1 V1) /V2
