P15 : Magnetism Flashcards
what are permanent magnets?
produce its own magnetic field ( doesnt lose magnetism)
what is an induced magnet?
when a magnetic material is placed in a magnetic field
- temporarily magnetic
magnetic field?
region around magnet where a force acts on another magnet or on a magnetic material
how are magnetic fields drawn?
- from north to south
- lines spaced out -> weaker attraction
what is the geographical north/south pole?
geographic north pole - magnetic south pole
geographic south pole - magnetic north pole
what is a solenoid/ how does it increase magnetic effect ?
long current-carrying coil used to generate a uniform magnetic field within its core
- coiling wire causes field to align/ form giant single field
how is the strength of magnetic field around solenoid increased?
- increase size of current
- increase no. coils
- adding iron core through centre of coils
how does iron core increase magnetic strength?
- easier for magnetic field lines to pass through air
what are electromagnets?
solenoids with an iron core
how can magnetic field of electromagnet be swicthed on/off?
On : - CURRENT FLOWS
off - no current flows
motor effect?
A wire with current flowing through it is placed in a magnetic field and experiences a force
- if wire is 90 degrees to magnetic field - experiences force
- if wire is parallel to magnetic field- no force
factors affecting force exerted in motor effect?
- increasing current in wire - increase magnetic field around wire
- use stronger magnets - increase field between 2 poles
- place wire at 90 degrees to magnetic field
- increase no. turns in coil
how to determine direction of force (thrust) on current carrying wire ?
Fleming’s left hand Rule
thumb - thrust
first finger - field
second finger - current
what is the right hand thumb rule?
- used to work out direction of magnetic field
how do electric motors rotate?
- current flows 90 degrees to direction of magnetic field –> magnetic field created around coil
- magnetic field from coil and from magnets interact
- results in force exerted on coil
- as current will flow in opposite directions in each side of coil, the force will move one side of coil up/down –> rotation until in vertical position (forces act up and down)
how to increase speed of rotation of coil D.C motors?
increasing current/stronger magnet
how is direction of rotation of coil changed?
- reverse direction of current
- reversing direction of magnetic field by reversing poles
what does a loudspeaker consist of?
a coil of wire wrapped around one pole of permanent magnet
what makes the coil oscillate in loudspeakers?
- an alternating current passes through the coil in loudspeaker
- creates changing magnetic field - current is constantly changing direction, so magnetic field is too
- magnetic field produced around coil interacts with field around magnet - exert force on coil
- as magnetic field direction is changing , force exerted on coil changes direction - makes coil oscillate
what is the generator effect?
When there is a relative movement between a conductor and a magnetic field/magnetic field changes a potential difference is induced across the conductor.
what happens when a wire (conductor) is put into a fixed magnetic field?
wire cuts through field lines
- induced Potential difference on wire
factors effecting induced potential difference?
-
speed at which wire,coil or magnet moves
- increase speed - increase rate at which magnetic field lines are cut–> MORE PD -
no. turns on the coils in wire
- more coils means more mganetic field lines cut –> MORE PD - size of coil
- strength of magnetic field
- orientation of poles on magnet - effects direction of pd
what is Lenz’s law?
The direction of an induced potential difference always opposes the change that produces it
- This means that any magnetic field created by the potential difference will act so that it tries to stop the wire or magnet from moving
uses of generator effect?
- generate AC in ALTERNATOR
- generate DC in DYNAMO
