electromagnetism, generators and transformers Flashcards
what is a magnetic field?
path taken by a freely moving North pole
what are magnetic field lines?
fill the space around a magnet where the magnetic forces work and where they attract or repel magnetic material.
how do you detect magnetic field lines?
iron fillings
what are the rules of a magnetic field line drawing?
arrows that come from north to south
field lines are more concentrated at the poles
where is the magnetic field the strongest?
at the poles where the field lines are more concentrated
how do you find the direction and shape of the magnetic field?
by plotting compasses
what is Flemming’s left hand rule?
helps remember the direction of motion in an electric motor
First finger - direction of the magnetic Field (N - S)
seCond finger - direction of the Current (+ - -)
thuMb - direction of Movement
what is the motor effect?
when a current-carrying wire or coil can exert a force on a permanent magnet
what happens when a current runs through the coil in an electric motor?
the coil experiences a force and moves
why does the direction of current have to be reversed every half turn in a moving electric motor?
because if you do not the coil comes to a halt and stops turning
how do you switch the direction of current every half turn?
by a split ring or commutator
how do you increase the size of a force?
increase stength of magnetic field
increase current
how do you increase the turning effect of an electric motor?
increase current increase turns on the coil increase strength of magnetic field increase area of the coil use an iron core
how is an induced voltage produced?
when a magnet moved into coil of wire
how id the direction of the induced voltage changed?
when the magnet is moved out of the coil again
is there an induced voltage if there is no current?
no
how do you increase an induced voltage?
move the magnet faster
add more turns to the coil
increase strength of the magnet
what happens if wire is moved down?
galvanometer goes to the left
what happens if wire is moved up?
galvanometer goes to the right
what happens if wire is moved sideways?
stays at 0
how do you find current direction in electromagnetic induction?
right hand rule
first finger - field lines
second finger - current
thumb - movement
how do you increase the size of an induced current or voltage?
increase speed of movement
increase strength of magnetic field
increase number of turns on the coil
increase area of coil
why is the current and voltage produced maximum when coil turns?
more field lines are cut per second
what is the national grid?
a network of power stations, transformers and cables which distributes electricity across the country
what does a step up transformer have more of than a step down transformer? what does this do?
more turns of wire on the coil
creates a larger induced voltage in the secondary coil
how does a transformer work?
alternating current/ voltage in the primary coil creates an alternating magnetic field through the primary coil. The iron core traps the magnetic field and links it to the secondary coil. The changing magnetic field through the secondary coil induces an alternating current/ voltage
why does an alternating voltage on the input have to be used?
to create an alternating magnetic field
