electric and magnetic fields Flashcards
what 2 poles attract
2 opposite poles
(north and south)
what 2 poles repel
2 of the same
(north and north OR south and south)
what are some examples of magnetic metals
iron
nickel
colbalt
steel
what do all the permanent magnetic metals do
attract other magnetic items
what do all the temporary magnetic materials do
only become magnetic when placed in a magnetic field and will quickly lose its magnetism when removed from the magnetic field
shape of magnetic field in a permanent magnet
from north to south
shape of magnetic field in a temporary magnet
same as permanent (north to south) except with a induced magnetic in
characteristics of uniform magnetic fields
the magnetic field lines are equidistant and parallel to each other
how to use a plotting compass
Put the magnet on a piece of paper and draw round it and place the compass on the paper near the magnet.
The needle will point in the direction of the field line at this position.
Mark the direction of the compass needle by drawing two dots - one at each end of the needle.
Move the compass so that the tail end of the needle is where the tip of the needle was in the previous position and put a dot by the tip of the needle.
Repeat this and then join up the marks you’ve made, you’ll end up with a drawing of one field line around the magnet.
Repeat this method at different points around the magnet to get several field lines.
how is there evidence of the earths core being magnetic
when they’re not near a magnet, compasses always point towards the Earth’s North Pole.
this is because the Earth generates its own magnetic field, shows the inside (core) of the Earth must be magnetic.
electromagnetism
an interaction that occurs between particles with electric charge via electromagnetic fields.
what does the strength of field depend on
size of the current and distance from the long straight conductor
real life examples of electromagnets
fridge doors
doorbells
MRI machines
explain an electromagnet
has a battery which is connected to wires which are connected to an iron core with wire wrapped around which is connected to the current
explain flemings left hand rule
first finger - magnetic field
middle finger - current
thumb - movement
simply line your hand up to the horizontal arrows direction and the vertical direction, that will position your thumb in the correct place
what does flemings left hand rule find
the direction of the force on the current carrying conductor
what’s the right hand rule and how is it done
point your thumb up in the direction of the current and curl your fingers, direction of fingers is direction of the field
what is a solenoid
a long coil of wire with an iron core which is a example of a electromagnet
what’s inside a solenoid
individual coils which add together a very strong almost uniform field along the centre of the solenoid and cancel to make the field outside weaker
what does a changing magnetic field induce
a potential difference in a conductor
what is a step up transformer
step the potential difference up (i.e. increase it)
They have more turns on the secondary coil than the primary coil.
what is a step down transformer
step the potential difference down (i.e. decrease it).
They have more turns on the primary coil than the secondary.
equation for transformers
Vp x Ip = Vs x Is
Vp - potential difference across primary coil
Ip - current across primary coil
Vs - pd across secondary coil
Is - current through secondary coil
explain the national grid
- starts with a power station
- moves into a step up transformer
- then step down transformer
- the home
what do transformers in the national gird produce
high P.D. and low current
what’s the second transformer equ
Vp / Vs = Np / Ns
what so step up and step down transformers do in the nation grid
Step-up transformers at power stations boost the p.d. up really high (400 000 V) and keep the current low.
Step-down fransformers then bring it back down to safe, usable levels at the consumers’ end.
what is the national grid
a network of wires and transformers which connect UK power stations to consumers
what does the national grid do
transfer loads of energy per second
what does the national grid do to reduce losses and make it more efficient
transformers are used
what is alternating current (AD)
an electric current that reverses its direction many times a second at regular intervals, typically used in power supplies.
what is direct current
an electric current flowing in one direction only.
what are magnetic forces due to
interactions between magnetic fields
what is flemings left hand rule equation
B x I x L
force:
magnetic flux density x current x length of wire
what does current carrying conductors experience
a force that an equal and opposite force acts on
what can current create and why
a magnetic effect due to the shape and direction of the magnetic field
