Magnetic fields

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• Created by: Sagaana
• Created on: 01-06-18 19:37
• Magnetic Fields
• What is Magnetic Field
• It is a region where a force is exerted on Magnetic material
• Go from north to south pole
• The closer they are the stronger the field
• There is magnetic field around a current carrying wire
• use right hand rule to work out the direction of the field line
• solenoid creates a field like a bar magnet
• This will experience a force when placed on a magnetic field
• the field around the wire and the fields cause by magnet add up creating a resultant field
• resultant force are close together creating a strong magnetic field which pushes the wire.(force acting on it )
• this force is perpendicular to both current and field
• There will be no force when current is parallel to the field line.
• you can work out the force using Flemings left hand rule
• Force on the wire is proportional to Flux Density
• TESLA  = The force Carrying a current of 1 amp at right angles to the magnetic field.
• This is the unti of flux density
• Charged Particle in Magnetic Field
• Force acts on a charged particle moving in a magnetic field.
• Charged particle in a magnetic field are deflect in a circular motion using Fleming Left hand Rule
• Second finger in Fleming's left hand rule will be for the direction of motion for a positive charge.
• when charge particle is negative the direction would be opposite to the negative charged particle
• Centripetal force on the charged particle will equal the force on charged particle when in a magnetic field
• radius increases the particle deflects less
• Radius decreases the particle deflects more
• Cyclotrons
• Made up two hollow Dees with a Perpendicular uniform magnetic fields and alternating p.d applied to the dees
• Charged particle follow semicircular path and leave the dee
• applied p.d accelerates the particle to the other dee
• particle speed increases so circular path has a bigger radius
• p.d is reversed so that accelerates to the other Dee and this process repeats until it leaves the cyclotron
• EM induction
• Magnetic flux= Total number field lines passing through the area (perpendicular)
• Magnetic flux density is the magnetic flux per unit area (density of magnetic field lines)
• Electromagnetic force= Electromagnetic Force is induced when in conductors that cut through the Magnetic Flux
• the magnetic flux passes through a coil changes.
• when coil part of a complete circuit induced current will flow through
• more coils bigger emf
• The change in flux linkage of one Weber per second will induce an electromotive force of 1 volt in a loop wire.
• cause by the elctrons experiencing a force at the ends of the rod.
• Alternators
• It is generator of alternating current
• it is one that changes with time
• voltage can go up and down in regular pattern
• rms current -just divide by root 2 this is the same thing for rms voltage.
• you can work out average power with this
• convert kinetic energy to electrical energy but rotating a coil in a magnetic field
• It has slip rings and brushes that connect to a external circuit
• The output Voltage and current change direction every half turn
• Induction Laws
• Faraday's Laws = the induced emf is directly proportional to the rate of the change of flux linkage/
• Lenz's Law = the induced emf is always in such a direction that opposes the change that caused it.
• This agrees with the conservation of energy.
• magnetic attraction against the force of  resistance = induced current.
• Transformers
• It uses electromagnetic induction to change the size of the voltage for a alternating current
• the alternating current in the primary coil produces magnetic flux
• This passes  through the core and links with the secondary coil
• the changing magnetic field in the secondary coil induces a voltage
• The voltage induces is proportional to the number of turns in that coil.
• Step-up Transformer- increases the voltage and step down does the opposite.
• They are not 100% efficient in practice.
• Eddy currents=the chnaging flux density induces the soft iron core which heats up
• lamination reduces the current that can flow.
• Resistance of coil = current flowing thru can also cause heating.
• use a low resistance wire
• Magnetisation of core = this requires energy to magnetise and demagnetise the core.
• use a magnetically soft material
• In the national grid transformers are used to reduce the power losses as power is transmitted through the cables at a very high voltage .