magnetism and the motor effect Flashcards
topic 12
do unlike magnetic poles attract or repel
attract
do like magnetic pole attract or repel
repel
Describe the uses of permanent and induced magnetic materials including cobalt, steel, iron and nickel
- fridge doors - permanent magnetic strip
- cranes - induced electromagnets
- doorbells - electromagnets that turn on and off
explain the difference between permanent and induced magnets
- permanent magnets produce their own magnetic field all of the time
- induced magnets only produce a magnetic field while they are in another magnetic field
an induced magnet :
only produces a magnetic field whilst they are in another magnetic field
Describe the shape and direction of the magnetic field around bar magnets and for a uniform field, and relate the strength of the field to the concentration of lines
- closer the lines, the stronger the magnetic field
- lines have arrowheads to show direction of the force exerted on a magnetic north pole
- arrowheads point from the north pole to the south
Describe the use of plotting compasses to show the shape and direction of the field of a magnet and the Earth’s magnetic field
- compasses have a small bar magnet inside them (needle)
1. place compass near magnet on paper
2. mark direction that the needle points
3. move compass to different positions in the magnetic field and mark directions
4. join the points to show field lines
does the needle of a plotting compass point to the norht or south pole of the magnet
south
Describe how to show that a current can create a magnetic effect
- by a current flowing through a long straight conductor
Explain how the behaviour of a magnetic compass is related to evidence that the core of the Earth must be magnetic
- the earth generates its own magnetic field
- so the compasses point towards the earths north pole (which is a magnetic south pole)
- shows the core of the earth must be magnetic
Describe the shape and direction of the magnetic field around bar magnets and for a uniform field, and relate the strength of the field to the concentration of lines - UNIFROM FIELD
- placing north and south poles of two bar magnets together creates a uniform field between the two poles
- the magnetic field is the same strength everywhere between the poles
a current can create a magnetic effect. relate the shape and direction of the magnetic field around a long straight conductor to the direction of the current
- shape is made of concentric circles perpendicular to the wire at the centre
- changing the direction of the current changes direction of the magnetic field
- larger the current through the wire/ closer to the wire you are. the stronger the field is
what does the strength of the field depend on
- size of current
- distance from long straight conductor
what is a solenoid
a long coil of wire and example is an electromagnet
what is an electromagnet
a magnet with a magnetic field that can be turned on and off using an electric current
what do the fields from individual coils inside a solenoid do
- cancel to give a weaker field outside the solenoid
- add together to form a very strong almost uniform fields along the centre of the solenoid
what does a current carrying conductor placed near a magnet experience
- a force
- an equal and opposite force acts on the magnet
- (magnetic forces are felt due to interaction between any two magnetic fields)
explain how magnetic forces are due to interactions between magnetic fields
- magnets interact feeling a magnetic force of attraction/ repulsion
- (the magnet and wire exert a force as two magnetic fields interact)
- when they interact the wire will be pushed away from the field between the pole at right angles to the wire direction and the field direction
how to use Fleming’s left hand rule
- point First finger on your left hand in the direction of the magnetic Field
- and seCond finger in the direction of the Current
- your thuMb will point in the direction of the force (Motion)
what does Fleming’s left hand rule represent
- relative directions of the force, current and magnetic field
equation to find the force on a conductor at right angles to a magnetic fields carrying a current
force on a conductor at right angles to a magnetic fields carrying a current (N) = magnetic flux density (T or N/A m ) * current (A) * length (m)
what is magnetic flux density
how many field (flux) lines in a region (this shows the strength of a magnetic field)
what is the motor effect
a current in a magnetic field that experiences a force
what is electromagnetic induction
induction of a p.d in a wire which is experiencing a change in magnetic field
