magnetism- induced potential and transformers + motor effect Flashcards
transformers
a transformer consists of two coils of wire:
- primary coil left hand side
- secondary coil right hand side
the two coils are completely separate
there is no way that electrical current can pass directly from one coil to another
the two coils are wrapped around an iron core
why is an iron core used
because its easily magnetised
primary coil is connected to an alternating current
as the current flows through the primary coil , it generates a changing magnetic field
this magnetic field is transmitted along iron core and passes through secondary coil
what happens when a changing magnetic field is passed through the secondary coil
a potential difference is induced
what does the iron core do
increases the strength of the magnetic field
why do transformers only work with an alternating current and not a direct current
because we need a changing magnetic field to induce a potential difference
a direct current produces a constant magnetic field and that does not induce a potential difference therefore it does not work in transformers.
if the primary and secondary coil both have the same number of turns
the potential difference in the primary coil will be the same as the potential difference in the secondary coil but it is only the case if the transformer is 100 percent efficient( if there is no energy wasted)
what if there are more turns in the secondary coil than in the primary coil
the potential difference induced in the secondary coil will be greater than the potential difference induced in the primary coil this is called a step up transformer as it steps up (increases) the potential difference
what if there are twice the number of turns in the secondary coil than in the primary coil
the potential difference in the secondary coil will be twice the potential difference in the primary coil
in a step down transformer, there are fewer turns in the secondary coil than in the primary coil
in a step down transformer, potential difference in secondary coil is less than potential difference in the primary coil
what if the number of turns in the secondary coil is halve the number of turns in the primary coil
the potential difference in the secondary coil will be half the potential difference in the primary coil
potential difference in primary coil/ potential difference in secondary coil=
number of turns in primary coil/ number of turns in secondary coil
a transformer has 200 turns in the primary coil and 50 turns in the secondary coil . a potential difference of 48v is induced in the secondary coil . calculate potential difference in the primary coil
200/50 = 4
48x4=192
192 V
a transformer has 100 turns in the secondary coil. it steps up the potential difference from 50v to 250v . calculate number of turns in primary coil
20 turns
50/250 x 100
power must be conserved
power of primary coil= power of secondary coil
power= potential difference in primary coil x current in primary coil
potential difference in secondary x current in secondary coil
it only applies if transformer is 100 percent efficient
a trasnformer has a potential difference of 200v and a current of 0.1A in the secondary coil the potential difference of the primary coil is 50v calculate current in primary coil
0.4A
when a current is produced around a conducting wire
a magnetic field is produced around the wire
how can we prove that there is a magnetic field around the wire
we can use a compass when the current is turned off the compass needle lines up with the Earths magnetic field.
if we turn the current on again, the compass needle deflects this proves that there is a magnetic field around the wire