Magnets Flashcards
(24 cards)
what is a magnetic field ?
region where magnetic materials experience a force
what is the uniform field ?
magnetic field of north and south bar magnets close together
How do you test for magnetic field patterns ?
can use multiple compasses to see magnetic field
can use iron fillings to see magnetic field (put magnet under paper with iron on top)
What is inducing magnetism ?
when a magnet goes near a magnetic material, the material acts a magnet, closer magnet is to material, the stronger induced magnetism
what happens to a current carrying wire ?
current carrying wire creates a magnetic field around
larger the current, stronger the magnetic field
direction of magnetic field depends on direction of current
what is a solenoid?
coil of wire with a strong and uniform magnetic field
What is an electromagnet?
current-carrying solenoid creates a strong and uniform magnetic field
field is just like a bar magnet field
ends of solenoid act as north and south poles
what is a hard magnetic material ?
difficult to induce magnetism, but keeps it permanently
steel for example
what is a soft magnetic material ?
easy to magnetise, loses induced magnetism quickly
iron for example
adding soft iron core to solenoid increases strength of magnetic field
explain how a motor turns
current flows in a wire creates magnetic field field interacts with permanent magnets creates a force on the wire use Fleming's rule to find force direction
what the fingers represent on FLHR
first finger = field
thumb = motion
centre finger = current
what is the direction of current
+ve to -ve
what is the direction of field lines
north to south
what is electromagnetic induction?
creation of voltage in a wire which is experiencing a change in magnetic field
what are the factors which speed up an electric motor ?
more current
more turns on coil
stronger magnetic field
add a soft iron core
how do loudspeakers work ?
A.C electrical signals are fed to a coil of wire in the speaker which is wrapped around base of cone
coil surrounded by perm magnet so force created and makes cone vibrate
what is the dynamo effect ?
using EI to transform kinetic energy into electrical energy for example :
electrical conductor moves through magnetic field
or changing magnetic field through a conductor
what would you use an ammeter for in the dynamo effect ?
show magnitude and direction of current
how to reverse induced current/voltage in dynamo effect ?
reverse movement direction
how to get a bigger voltage from dynamo effect ?
increase magnet strength
speed of movement
number of turns on coil
how do transformers work ? (5mrk)
Alternating current causing changing magnetic field in soft (easily demagnetised) iron core. Changing magnetic field induces current. Step - up used to boost voltage and step - down used to reduce voltage
difference between coils on step up/down transformers
step - down has more coils on primary
step - up has more on secondary
transformer coils equation
Vp / Vs = Tp / Ts
transformers are nearly 100% efficient so …
Voltage 1 x Current 1 = Voltage 2 x Current 2
