magnetism and electromagnetism
- Created by: Sc1602
- Created on: 18-03-18 08:40
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- magnetism
- poles
- where forces are strongest
- when magnets brought close together they exert force on each other
- like poles repel
- unlike poles attract
- where forces are strongest
- permanent magnet
- own magnetic field
- induced magnet
- becomes a magnet when placed in a field
- causes a force of attraction
- once removed from field quickly loses most/all magnetism
- magnetic fields
- region around magnet where force acts on another magnet or magnetic material
- force between magnet and magnetic material is attraction
- iron
- steel
- nickel
- cobalt
- force between magnet and magnetic material is attraction
- strength
- depends on distance from magnet
- strongest at poles
- direction
- given by direction of force that would act on a north pole at that point
- line from north to south pole of magnet
- compass
- contains small bar magnet
- needle points in direction of earth's field
- region around magnet where force acts on another magnet or magnetic material
- electro-magnetism
- when current flows through a conducting wire a field is produced around the wire
- strength
- current
- distance
- shaping wire into a solenoid
- increases strength of field
- magnetic field is strong and uniform
- field is a similar shape to bar magnet
- adding iron core increases strength of field
- electro- magnets
- solenoid with iron core
- motor effect
- when a current carrying conductor is placed in field and magnet and conductor exert a force on each other
- Fleming's left hand rule
- for a conductor at right angles to field and carrying a current, F=B I l
- electric motors
- a coil carrying a current in a magnetic field tends to rotate
- loud-speakers and head-phones
- use motor effect to convert variations in current in circuits to pressure variations in sound waves
- induced potential
- if an electrical conductor moves relative to a magnetic field or if there is a change in the field around a conductor, a pd is induced across the ends of the conductor
- if the conductor is part of a complete circuit, a current is induced in the conductor
- this is the generator effect
- used in an alternator to generate ac
- used in a dynamo to generate dc
- used in microphones to convert pressure variations in sound waves into variations in currents
- this is the generator effect
- induced current generates a field which opposes the original change
- if the conductor is part of a complete circuit, a current is induced in the conductor
- if an electrical conductor moves relative to a magnetic field or if there is a change in the field around a conductor, a pd is induced across the ends of the conductor
- trans-formers
- consist of primary and secondary coils wound on an iron core
- iron used as its easily magnetise-d
- Vp/Vs=Np/Ns
- in a step up trans-former Vs is greater than Vp
- in a step down trans-former Vs is less than Vp
- if 100% efficient, electrical power output would equal electrical power input
- Vs x Is = Vp x Ip
- poles
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