p15 Flashcards
what can any iron or steel object do
can be magnetised or demagnetised
what are permanent magnets usually made of
steel as it does not lose its magnetism very easily
what is a magnetic field
the region around a magnet in which a magnetic material experiences a force
draw the magnetic field lines around a bar
what happens when an unmagnetised material is placed in a magnetic field
induced magnetism - the material becomes magnetised
what will induced magnetism always do
cause a force of attraction between the existing magnet and the unmagnetised magnet
how is a magnetic field induced around a wire
when the current passes along the wire
what is the magnetic field around a wire like
series of concentric circles perpendicular to the wire
what is a solenoid
long coil of insulated wire
what is the magnetic field of a solenoid like
the magnetic field lines inside the solenoid are parallel to the axis of the solenoid and are all in the same direction
what happens when you reverse the direction of the current for a single wire and a solenoid
reverses the direction of the magnetic field
what happens when you increase the current for a single wire and a solenoid
increasing current increases the strength of the magnetic field
what is an electromagnet
a solenoid in which an insulated wire is wrapped around an iron bar
why are electromagnets useful
they allow a magnetic field to be switched on or off by switching the current on and off
what devices are electromagnets used in
scrapyard cranes
circuit breakers
electric bells
how does a circuit breaker work
too great a current makes the electromagnet open a switch which cuts the current off
how does an electric bell work
when the bell is pushed on, an electromagnet attracts an iron armature which hits a bell
because the iron armature is pulled away from the make or break switch the electromagnet loses its magnetism and the armature springs back
what is the motor effect
a wire carrying an electric current inside a magnetic field may experience a force
when is the force at its greatest in the motor effect
if the wire is at an angle of 90 degrees to the magnetic field
what is magnetic flux density
a measure of how strong the magnetic field is
