unit 9 - magnets and currents Flashcards
(23 cards)
what kinds of material do all strongly magnetic materials have
iron, nickel, or cobalt
what is a soft magnetic material, and an example
relatively easy to magnetize but their magnetism is only temporary.
Iron
what is a hard magnetic material, and an example
difficult to magnetize but do not readily lose their magnetism.
where magnetism comes from
atomic magnets line up each other that they get stronger as more of them line up in the same direction
describe field line
from N pole to S pole
strongest where the field lines are closest together
what is the neutral point
the point where the fields from magnets cancel each other
feature of the magnetic field produced by a current-carrying coil
the field is similar to the one from bar magnet,
increasing the current increases the strength of the field
increasing the number of turns on the coil increases the strength of the field
how to demagnetise a magnet
slowly pull out through solnoid which alternating current is passing
hammer the magnet
heating it at high temperature
what is the core made of
iron
purpose of relay
turn on the current in a much powerful circuit using a small switch
what is the thumb, first and second finger stand for in Flemming’s left-hand rule
thumb- thrust
first - field
second - current
when do we apply Flemming’s left-hand rule
when the current is causing the motion
how can the force increase in the experiment using flemming’s left hand rule
increase current
stronger magnet
more length of wire in the field
the purpose of split-ring commutator in electric motor
swaps the positive and negative connection every half turn so that the direction of the current swaps every half turn. force in the coil will always act in the same direction
what is a galvanometer for
to detect vert small currents
describe what happens when the bar is pushed into a coil
an e.m.f. is induced
e.m.f. and the current can be increased by :
moving magnet faster
using a stronger magnet
increasing the number of turns on the coil
what is Lenz’s law
the induced current always flows in a direction such that it opposes the change which produced it
when do we use Fleming’s right-hand rule
when the motion is causing the current
what thumb, first and second finger stand for in Flemming’s right-hand rule
thumb- motion
first - field
second - current
formula for transformer
v1i1 = v2i2
difference between step up and step down transformers
step up - the output voltage is more than input
step down - the output voltage is less than input
what is the core of transformer made of
iron
why is the power transmitted at very high voltage
if voltage increases, current decreases
if there are a lot of current then many energy will be lost due to the heat
also current is reduced, thinner wire can be used so that cheaper cables can be used
