Unit 7 - Magnetic Fields Flashcards
(30 cards)
Magnetic rule of attraction
Opposite poles attract (north attracts south)
Similar poles repeal (north repels north, south repels south)
Describe the properties of a magnetically hard material
A magnetically hard material retains its magnetic properties for a long period of time/ permanently
They’re difficult to demagnetise.
Describe the properties of magnetically soft materials
A magnetically soft material looses its magnetic properties almost as soon as it leaves a magnetic field.
What are magnetic field lines
They represent the shape and direction of a magnetic field
They always go from north to south
How to induce magnetism in a magnetic material
Stroke it repeatedly with a magnet to align the domains
Place it in a magnetic field to align the domains
What types of materials are attracted to magnets and can be magnetised
Iron / steel
Nickel
Colbalt
Copper
Magnetic field lines always go from
North to south
describe experiments to investigate the magnetic field pattern for a permanent bar magnet and that between two bar magnets
To track field lines you can use iron filings, which are magnetic materials, which will line up along the magnetic field. and you can use compasses which will show that the lines go from north to south.
How to produce a magnetic field (in a conductor)
By passing an electric current through a conductor it will produce a magnetic field around it
Describe the constriction of electromagnets
A piece of wire is wrapped around a soft magnetic material. When there is a current in the wire, a magnetic field is induced in the metal. Electromagnets can be turned on and off by turning on/off the current
How to increase the strength of an electromagnet
Increase the current
Increase the number of coils of wire around the soft iron core
Magnetic field lines around a straight coil
circles round the wire (right hand thumb rule for direction)
Magnetic field lines around a solenoid
Similar to a bar magnet
Describe how to use two permanent magnets to produce a uniform magnetic field
If you put two bar magnets together with their north and south touching, then they will form the same magnetic field as if there were one bar magnet.
‘hold two opposite poles close to each other so that they attract as this makes a uniform magnetic field’
Relationship of a transformer
Vp/Vs = Np/Ns
Input voltage / output voltage = primary turns / secondary turns
Relationship for 100% efficiency
Input power = output power
VpIp = VsIs
Primary voltage X primary current = secondary voltage X secondary current
When will there be a force on a charged particle (magnetic field)
The is a force on a charged particle when it moves into a magnetic field as long as it’s motion is not parallel to the field
What is the motor effect
A wire carrying current in a field experiences force
Why does the motor effect happen
The field from the current “squashes” the external field from the magnets. This “catapults” the wire out of the field
How does an electric motor work
A simple electric motor can be built using a coil of wire that is free to rotate between two opposite magnetic poles. When an electric current flows through the coil, the coil experiences a force and moves.
The direction of the current must be reversed every half turn, otherwise the coil comes to a halt again. This is achieved using a conducting ring split in two, called a split ring or commutator. A coil of wire is used with lots of turns to increase the effect of the magnetic field.
How does a loudspeaker work
When a fluctuating electric current flows through the coil, it becomes a temporary electromagnet, attracted and repelled by the permanent magnet. As the coil moves, it moves the cone back and forth, pumping vibrations (sound waves) into the air.
Flemings left hand rule
Left hand
Pointer finger goes in the direction of the field (north to south)
Middle finger goes in the direction of the current (positive to negative)
Thumb is the direction of the force (where the wire moves to)
How to increase the force of a current carrying conductor
Increase the size of the current
Increase the strength of the field around it
How to induce voltage in a conductor or coil
Voltage is induced in a conductor or coil when it moves through a magnetic field or when a magnetic field changes through it. A voltage will only be generated if the wire moved perpendicular to the magnetic field (must cut across lines)
