magnetic fields Flashcards
what is a magnetic compass?
a needle pivoted at its centre
explain how to investigating bar magnets?
suspend a magnet and mark the end that points north as N. then hold a second magnets N against the suspended magnet. it should repel and switch sides.
what is the general rule with bar magnets?
like poles repel, unlike poles attract.
any iron or steel object can be?
magnetised
explain how to find the magnetic field around a bar magnet
place the magnet under a sheet of paper and sprinkle iron filings on top. they will form a pattern of lines. they will be more concentrated at the poles, because it is stronger here.
explain what a plotting compass will do?
when placed in the magnetic field, it will point away from the north pole and towards the south.
the direction of a line of force is
always from north to south
an unmagnetised magnetic material can be magnetised by?
placing it in a magnetic field
what material is most likely to be used for permanent magnets?
steel
what is a solenoid?
a long coil of insulated wire.
the magnetic field in a solenoid is produced in and around when?
current is passed through a wire
the magnetic field in a solenoid can be increase in strength by?
increasing the current
the magnetic field in a solenoid can reverse its direction by?
reversing the current
to increase the force in a electromagnet you can?
increase number of coils
add an iron core
increase the current
move magnetic material closer
the magnetic field inside a solenoid is?
strong and uniform
what is an electromagnet?
a solenoid in which the insulated wire is wrapped around an iron core
list some uses of electromagnets
electric bell, circuit breaker, scrapyard crane
how does an electromagnetic work in some of the things it does?
it attracts an iron armature, each opens a switch
explain a practical to test the strength of an electromagnet
use an electromagnet to hold a flat iron bar. suspend the bar and measure the smallest amount of current needed to hold it. then increase weight and repeat readings. repeat and after increasing amount of turns. plot results that draw conclusions about what factors affect strength.
safety: make sure it does not get too hot.
the size of a force can be increased by?
increasing current
using a stronger magnet
explain flemmings left hand rule
thumb: movement
1st finger: current
2nd finger: field
you can work out the direction of force from this.
what is the equation for magnetic flux density?
force (N) = magnetic flux density (T) x current (A) x length (M)
what is magnetic flux density a measure of?
the strength of a magnetic field
what is the unit for magnetic flux density
tesla
