chapter 15- motors, generators and transformers Flashcards
magnetic materials
iron steel cobalt nickel
which way do magnetic field lines go
north to south
the closer together…
the stronger the magnetic field
how do compasses show the direction of magentic field
-compasses will point in direction of magentic field
-when not in a magnetic field they will always point north
permanent magnets
have their own magnetic field
induced magnets
magnetic materials that turn into magnets when they are put into a magnetic field
how do you increase the strength of a solenoid
-increase loops
-increase current
-put an iron bar inside the solenoid
the motor effect
when a current carrying wire has a magnetic field. When current carrying conductor is placed in a magnetic field, so that it cuts line of magentic force, the magnet and the confuctor exert a force of eachother.
in the motor effect the force is:
-increased if the current or strength of MF is increased
-at right angles to the direction of the magnetic field to the wire
-reversed if the direction of the current or MF is reveresed
-zero if the wire is parallel to the magnetic field
motor effect loudspeaker
-current creates a magnetic field around the coil
-which interacts with the permanent magnet
-producing a resultant force causing the coil/cone to move
-when the direction of the current reverses, the direction of the resultant force reverses, producing a sound wave
generator effect
-effect of inducing a potential difference across the ends of a conductor using a magnetic field
-when a conductor moves relative to a magnetic field (cuts through), the conductor is in a changing MF
simple ac generator
made up of a coil that spins in a uniform magnetic field
difference between dc and ac
dc- direct current, flows in one direction
ac-alternating current, changes direction
moving coil microphone
sound waves make the coil vibrate in the magnetic field, so a varying p.d is induced
the faster the coil rotates
-the greater the frequency (number of cycles per second) of the alternating current
-the larger the peak value of the altnerating current
traditional transfromer
-works only on a.c, because changing magnetic field is necessary to induce a.c in the secondary coil
switch mode transformer
-lighter and smaller than an ordinary transformer, operate at high frequency
transformers
-change the p.d but only on alternating currents
-they all have 2 coils of wire, the primary and secondary, joined with an iron core
-when an alternating pd is induced across the primary coil, the iron core magnetises, and demagnetises, induces changing pd in the secondary coil
-if the second coil is part of a complete circuit, this causes a current to be induced
step up transformer
-makes the pd acorss the secondary coil higher than the pd acorss the primary coil, secondary coil has more turns than primary coil
step down transformer
makes the pd across the secondary coil lower than the pd on the primary coil, secondary coil has fewer turns than primary coil
the higher the grid…
potential difference, the greater is the efficiency of transferring electrical power through the grid
what is a magnetic field
region of space around a magent where a magentic material will experience a force
the size of the induced potential difference increases when
-speed of the movement increases
-strength of magnetic field increases
-number of turns on coil increases
-area of coil increases
step up and step down transformers
increase the voltage before the distrubution lines and reduce it at the end to produce a safer voltage for local consumers
