magnetic fields

cyclotron

protons are produced in the centre and travel in a circular pa#th due to magnetic fields applied in this region. Protons are accelerated in the space between the dees by alternating electric fields applied in this region, increasing the radius o their path. At the max radius, the protons are released. This can produce extremely high proton velocities as they are accelerated many times

velocity selector function

gives charged particles a specific speed

cyclotron function

accelerates charged particles to very high speeds

mass spectrometer

separates ions based on their mass/charge ratio

velocity selector

a device that allows only charged particles with a specific velocity to pass through undeflected. it uses both electric and magnetic fields that act at right angles to each other and to the direction of motion of the particles

mass spectrometer stages

ionisation, acceleration, deflection, detection

mass spectrometer ionisation stage

high energy electrons knock out electrons of atoms causing them to become positive ions

mass spectrometer acceleration

positive ions accelerated by an electric field, all ions gain the same ke, light ions move faster

mass spectrometer deflection

ions pass into a magnetic filed, force on moving charges causes circular motion, r=mv/Bq, deflection depends on the mass/charge ratio, smaller m/q-more deflection

mass spectrometer detection

ions hit detector, gain electrons, produces current, current = number of ions - relative abundance

define magnetic flux

the product of magnetic flux density and the cross-sectional area perpendicular to the direction of the magnetic flux density

faraday’s law

the size of the induced emf in a circuit is equal to the rate of change of magnetic flux linkage through the circuit

factors affecting size of emf induced

speed of relative motion, size of magnetic flux density, length of conductor

factors affecting direction of induced emf

direction of relative motion, orientation of magnetic field

lenz’s law

the induced emf acts in such a direction to produce effects that oppose the change causing it

magnet dropped down hollow conductive tube

currents are induced in the tube the tube by the changing flux linkage, the induced currents create induced magnetic fields, the induced magnetic fields oppose the motion of the magnett, the magnet experiences a resistive force so it slows down

em braking

apply a magnetic flux density across a spinning brake with an electromagnet, disc moves through the magnetic field, meaning flux lines are cut by the disc, currents are induced in the disc by the changing flux linkage, the induced currents create induced magnetic fields, the induced magnetic field opposes the motion of the disc so it slows down

define transformer

a devices that changes high alternating voltage at low current to low alternating voltage at high current, and vice versa

what is a transformer made up of

a primary coil, secondary coil, iron core

purpose of soft iron core

the soft iron core is needed as it focuses and directs the magnetic field from the primary to secondary coil

why is soft iron used for transformer core

can easily be magnetised and demagnetised

how transformer workds

in the primary coil, an alternating current produced from an alternating voltage goes through the coils, this creates an alternating magnetic field inside the iron core and therefore a changing magnetic flux linkage, a changing magnetic field passes through to the secondary coil through the iron core, this results in a changing magnetic flux linkage in the secondary coil and from faraday’s law, an emf is induced

in the transformer core, inefficiencies appear from:

induced eddy currents, the reversal of magnetism, poor insulation between the primary and secondary coil

eddy current

unwanted circulating current that gets induced in the core whenever there is a change in the magnetic field. They waste energy as heat in the core

how to reduce energy loss in core

laminating the core to reduce eddy current (increases resistance)

how to reduce energy loss in coils

use conductors with low resistance, use thick wires

rmv voltage

the equivalent DC voltage that produces the same power as the AC signal