Magnetism Flashcards
Magnets.
A ferromagnetic object that produces a magnetic field.
Field emanates from north pole, re-enters at south pole.
Types of magnet.
Permanent magnet - retains its magnetic properties permanently. ‘Hard iron’
Electromagnet - Able to vary their field strength according to strength of electric field. ‘Soft iron’.
Field strength can be controlled through adjustment of current.
Wrapped with a coil.
The relay
Used in modern aircraft.
Form remote switches.
Uses small voltage/current to close a contact therefore controlling large voltage/current.
By turning off control current, soft iron demagnetises and a spring opens the contacts which turns off high current circuit.
For larger current/voltage the term ‘contactor’ may be used.
A coil wrapped around a fixed ferrous core creates an electromagnetic force when the coil is energised. This closes a switch to allow high current to pass through a second circuit.
The solenoid
Operates in similar manner to relay but instead the permanent magnet core is now moving.
With control current switched on, magnetic core is attracted into the coil field and compresses a return spring.
With control current switched off, core is returned to original position.
Normally used as switching and control function.
These are ideal for locking mechanisms, piston engine starter motors and solenoid type fuel injectors.
Considered as heavy duty devices with relay considered as light duty.
Ferrous metal core moves when a current is caused to flow in a coil of wire wrapped around it.
Electromagnetic induction.
voltage generated within a conductor placed in close proximity to a magnetic field.
Maximum induction occurs when the conductor and field perpendicular.
Induction stops when the conductor or magnet stop moving or conductor is moving along a field line.
What can one current carrying wire do to another wire close to it?
Induce a current.
