dynamos and transformers Flashcards
(15 cards)
what is generated in a dynamo
a direct current
what can be used to generate a direct current in a dynamo
the generator effect
what is an alternator
a rotating coil in a magnetic field with two slip ring commutators
whats the difference between a dynamo and an alternator
dynamo quite similar to alnternator but instead of using two seperate slip rings it using two split ring commutators
how does dynamo work
-as coil rotates, it cuts through field lines inducing a potential difference between the end of the coil
-the split ring commutator changes connections between the brushes and coil every half turn in order to ensure that the current leaving the dynamo stays in the same direction
-induced potential difference does not reverse its direction
-instead, it varies from zero to a maximum twice each cycle of rotation whilst never changing its polarity
-it can either always be positive or always be negative.
what does a transformer consist of
primary coil, secondary coil, iron core
what is a transformer used for
changing the value of an alternating potential difference which is achieved through the generator effect
how can you increase current
-use a stronger magnet
-move a wire more quickly
-have more turns on the coil
what does a split ring commutator do
keeps the current in one direction
what does a slip ring commutator do
changes the direction of the current every half turn
how does a transformer work
-alternating current is supplied to primary coil
-as current is continually changing direction it produces a magnetic field around primary coil
-iron core is easily magnetised so changing magnetic field passes through it
-now theres a changing magnetic field inside the secondary coil
-this changing filed cuts through the secondary coil inducing a potential difference
-as magnetic field is continually changing, potential difference induced will be alternating
-alternating potential difference will have same frequency as alternating current supplied to primary coil
-if secondary coil is part of a complete circuit it will cause alternating current to flow
what does a transformer do ?
-changes size of an alternating potential difference
-decrease high voltage electricity used in power lines to decrease voltage used in houses
-increase potential difference of electricity before its transmitted across national power grid
what does a step up transformer do
increases potential difference of a power source so has more turns on secondary coil than on primary coil
what does a step down transformer do
decreases potential difference of a power source so has more turns on secondary coil than on primary coil
