Topic 12 - Magnetism and the motor effect Flashcards
All magnets have two
Poles
Two poles of magnets
Norht and south
Magnets produce
Magnetic fields where other magnets or magnetic materials experience a force
Unlike magnetic fields
Attract
Like magnetic fields
Repel
Magnetic fields can be shown by drawing
Field lines
Magnetic field lines rules
Always north to south
Closer the lines, stronger the magnetic field
The magnetic forces are strongest at the
Poles
When a north and south pole are placed near eachother
A uniform field is created where the magnetic field strength is the same everywhere between the poles
Compasses show magnetic field because
They have magnets inside that always line up with the magnetic field its in.
If the way the compass faces is plotted around a magnet, the magnetic field direction can be plotted
When not near a magnet, compasses always
Point towards the earths north pole because the earth creates it own magentic field.(north poleis actually the magnetic south pole)
Compasses show that the earths core is
Magnetic
Main three magnetic elements are
Iron, nickel, cobalt
The magnetic force between a magnet and magnetic material is
Always attractive
Permanent magnets are
Objects that always produce their own magnetic field
Induced magnets are
Objects that only produce a magnetic field when in another magnetic field
Magnetically soft materials are
Induced magnets that lsoe their magnetism quickly after being out of a magnetic field
Magnetically hard materials are
Objects tat lose their magnetism slowly
When a current flows through a long straight conductor
A magnetic field is created around it
The magnetic field induced by a current is
Made up of circles perpendicular to the wire
Rule to fidn magentic field direction from current
Right hand thumb rule
Direction of current is direction of thumb
Fingers curled in magnetic field direction
The strength of current induced magnetic field is dependant on
The current travelling through the wire, and the distance from wire
A solenoid is
A long coil of wire with lots of loops
The fields from individual coils in solenoids
Add together to form a very strong almost uniform field inside the solenoid
Cancel out to give a weaker field outside the solenoid
A solenoid is an example of an
Electromagnet. because it forms a field similar to a bar magnet, and can be turned on and off with current
When a current carrying conductor is placed near a magnet
It experiences a force and an equal and opposite force is exerted on the magnet
For a wire to experience the full force in a magnetic field
It needs to be 90*
The rule that shows current, magnetic field and force when a wire is interactign with a magnet
Flemings left hand rule
Thumb facing up shows current direction
Fisrt finger right shows magnetic field
Second finger facing towards you shows force on current carrying conductor(eg wire)
Force(N) =
Magnetic flux density x Current(A) x Length of wire(m)
A simple dc motor works by
Having two magnetic poles and a coil fo wire between them.
A force is exerted on the opposite side of coil so it spins
A split ring commutator is used to ensure the coil keeps spinning, because if there wasnt a change in charge travelling through, the forces would keep swapping and it wouldnt spin
