ELECTROMAGNETISM Flashcards
what do the magnets produce
magnetic fields
what is a permanent magnet
permanent magnets produce their own magnetic field and the magnetic field cannot be turned on and off
what is an induced magnet
they are magnetic materials that turn into a magnet when theyre put into an magnetic field
the force between the permanent and induced magnets is always
attractive
what happens when you take away the magnetic field from induced magnets
the induced magnets quickly lose their magnetism and stop producing a magnetic field
give two differences between permanent and induced magnets
permanent magnets produce their own magnetic field
induced magnets become magnets when put in an magnetic field
the force between permanent and induced magnets is always attractive
the force between two permanent magnets can be attractive or repulsive
the force between two permanent magnets can be
attractive or repulsive
when a current flows through a wire
a magnetic field is created around the wire
what is a solenoid
it is a coil of wire
electromagnets can be
turned on and turned off
How can the motor effect happen
It happens when you put a current carrying wire in a magnetic field
This causes the magnet and the conductor to exert a force on each other
What three things does the force acting on a conductor in a magnetic field depend on
Magnetic flux density
Size of the current
The length of the conductor that’s in the magnetic field
How do you find the direction of the force
Flemings left hand rule
What does your index finger represent in Flemings left hand run
Direction of
What does your middle finger mean in Flemings
The direction of the current
Force=…. (electromagnetism)
F=BIL
FORCE=MAGNETIC FLUX DENSITYCURRENTLENGTH
Units for F=BIL
(F)FORCE= N
(B)MAGNETIC FLUX DENSITY= T-Tesla
(I)CURRENT=A
(L)LENGTH= M
how does a loudspeaker convert electrical signals into sound waves
a coil of wire carrying an alternating current is wrapped around a pole of a permanent magnet which is surrounded by the other pole
when a current flows through the wire this causes a force which moves the cone in one direction
when the current reverses the force is reversed and the cone is moved in the opposite direction
this makes the cone vibrate which vibrates the air around it to create a sound wave of the same frequency as the alternating current
generator effect
using a mag field and a force on a wire to produce a current
what are generators Generators rotate a coil…..
generators rotate a coil in a magnetic field
as the coil spins a current is induced in the coil, this current changes direction every half turn
they have slip rings and brushes so the contacts don’t swap every half turn
so they produce an alternating current
dynamos
work in the same way as generators but they have split ring commutators
this swaps the connection every half turn to keep current flowing in the same direction
what are transformers
transformers change the size of the potential difference of an alternating current
they have two coils of wire a primary and secondary coil joined with an iron core
what is a step up transformer
step the potential difference up, they have more turns on the secondary coil than the primary coil
what is a step down transformer
step the potential difference down,
they have more turns on the primary coil than the secondary coil
equations for transformers
Vp/Vs=Np/Ns
input pd/output pd=no of turns on primary coil/no of turns in secondary coil
VsIs=VpIp
Pd across secondary coilcurrent thru sec coil= pd across prim coil current thru prim coil
how do you make an electromagnet stronger
more current
more coils
add a soft iron core
how do you make the motor affect larger
more current
stronger magnet
use more wire (more coils)
how do you make the generator effect larger
bigger force eg move wire faster
stronger magnet
more coils
types of electromagnets
scrapyard crane
relay switch
electric bell
motor effect example
a motor
generator effect examples
dynamo and alternator
combination of m and g effect
microphone-sound—electrical (motor effect)]
loudspeaker- electrical—sound (generator effect)
transformers
is an alternator AC or DC
AC
is an dynamo AC or DC
DC
a split ring commutator turns….
DC to AC
examples of permanent magnets
horseshoe magnet
bar magnet
detecting magnetic fields
place the plotting compass near the magnet on a piece of paper
mark the direction the compass needle points
move the plotting compass to many different positions in the magnetic field, marking the needle direction each time
join the points to show the field lines
