Magnetic fields
- Created by: Sagaana
- Created on: 01-06-18 19:37
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- 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
- TESLA = The force Carrying a current of 1 amp at right angles to the magnetic field.
- this force is perpendicular to both current and field
- resultant force are close together creating a strong magnetic field which pushes the wire.(force acting on it )
- the field around the wire and the fields cause by magnet add up creating a resultant field
- 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
- Second finger in Fleming's left hand rule will be for the direction of motion for a positive charge.
- Charged particle in a magnetic field are deflect in a circular motion using Fleming Left hand Rule
- Cyclotrons
- used in medicine e.g radioactive traces for radiotherapy
- 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
- particle speed increases so circular path has a bigger radius
- applied p.d accelerates the particle to the other dee
- Force acts on a charged particle moving in a magnetic field.
- 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.
- the magnetic flux passes through a coil changes.
- 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
- rms current -just divide by root 2 this is the same thing for rms voltage.
- voltage can go up and down in regular pattern
- it is one that changes with time
- 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
- It is generator of alternating current
- 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.
- This agrees with the conservation of energy.
- 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.
- the changing magnetic field in the secondary coil induces a voltage
- This passes through the core and links with the secondary 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
- Eddy currents=the chnaging flux density induces the soft iron core which heats up
- In the national grid transformers are used to reduce the power losses as power is transmitted through the cables at a very high voltage .
- What is Magnetic Field
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