P4 Flashcards
north pole field lines
go outwards
south pole field lines
go inwards
how to see magnetic field patterns
Put magnet under a piece of paper + scatter iron fillings on top, they will align themselves w the field lines
how to see magnetic field patterns with a compass
- Put magnet on paper
- place compass on the paper next to the mag
- mark dots where the needle is pointing to
- move compass to point and repeat at diff points
- join them up
Permanent magnet
All domains (small magnetic regions) line up always
Induced magnet
When in a magnetic field, regions that aren’t lined up, line up and become magnetic
how does a magnetic compass prove the Earth’s core must be magnetic
Compasses always point north when they aren’t near a magnet - evidence that earth has a magnetic north/south pole
Symbol for current going towards you + direction of field lines
dot, acw
Symbol for current going away from you + direction of field lines
cross, cw
rule to find out direction of magnetic field around a current
Right hand rule
fleming’s left hand rule
thumb - force
First Finger - Field
seCond finger - Current
Motor components
- current carrying coil between 2 opposite poles
- split ring commutator
- coil spins
split ring commutator
swaps contacts every half turn to keep the motor rotating the same direction
how to reverse the direction of the motor
reverse current/reverse fields
Electromagnetic Induction components (generator principle)
- Induced p.d. produced if wire is in a changing magnetic field
- field lines need to be CUT to induce p.d.
- move magnet in and out of coil of wire/ or move wire in magnet
How to increase induced p.d.
- more wire (induce p.d. in each loop so total p.d. increases)
- move wire faster
- stronger magnetic field (as you will be cutting more field lines p second)
alternator
type of generator that produces ALTERNATING p.d.
how does an alternator work
- Coil of wire spins between poles of a magnet
- slip rings used to produce perfect a.c.
Dynamo
type of generator that produces a DIRECT CURRENT
how does a dynamo work
Same arrangement as a motor - SPLIT ring commutator used
Basics of transformers
- Alternating p.d supplied = a.c. in p coil = field lines around coil continually change
- this produces a changing magnetic field in the iron core
- which in turn induces a changing p.d. in the secondary coild
In a transformer power always…
is equal
primary p.d x current = secondary p.d. x current
how does a dynamic microphone work
(use electromagnetic induction) ,
- sound wave is a pressure wave, as it hits the diaphragm, areas of compressions (high p) push it in and areas of low pressure (rarefaction) pull it ou
- as diaphragm moves in + out so does coil(has magnet in the centre)
- p.d. induced at the ends = electrical signal produced by a microphone
How does a loudspeaker work
(like a motor)
- changing p.d = changing current
- The coil is inside a permanent magnets magnetic field so it experiences a changing magnetic force
- diaphragm attached to coil therefore moves in + out = produces a sound wave of the same freq the diaphragm vibrates
Why are isolating transformers used?
To prevent direct contact w live wire and socket = reduces risk of electrocution
