Replace the loop of wire with a solenoid as shown in Fig 20.7(c). Close the switch. Use the compasses to map the shape of the magnetic field around the solenoid.
Observation The shape of the magnetic fields are illustrated in Fig 20.8(a), (b) and (c).
Straight wire
Loop of wire (above card)
Solenoid (above card)
Loop of wire (below card)
(a) (b) Fig 20.8 (c)
Solenoid (below card)
SCIENCE,TECHNOLOGY & SOCIETY
Electromagnets and their uses An electromagnet is a magnet constructed from a soft iron core with a coil of wire wound around it.A magnetic field is set up when an electric current is passed through the wire and disappears when the current stops.
They are used in many applications, including:
Scrap yards, electromagnetic relays in circuits, MCBs, loudspeakers, tape recorders, particle accelerators and maglev trains.
A maglev train Magnetic Flux Density
MAGNETIC FLUX DENSITY Magnetic flux density (B) is a measure of the strength of the magnetic field.
It is a vector quantity with an SI unit of tesla (T). Its direction is along the field lines from north to south.
A magnetic flux density of 1 tesla will cause a force of 1 newton on a conductor carrying a current of 1 ampere when 1 metre of that conductor is within the field. 1 T 1 N A1 m1
Force on a Current-carrying Conductor
in a Magnetic Field When the flow of current in a conductor is perpendicular to the magnetic field:
