how to magnetise and demagnetise steel
magnetise:
put inside a solenoid
connect solenoid to d.c. supply
switch on
demagnetise:
put inside a solenoid
connect to a.c. supply
withdraw rod from solenoid/slowly reduce current to zero
DO NOT switch off and take rod out directly, as then the magnet will have magnetic
field which was created by the solenoid at the time of switching off.
OTHER METHODS:
pound with hammer
heat until red hot
experiment to determine magnetic field pattern
use of compass/suspended small magnet
observe needle/magnet on one field line
observe needle/magnet on another field line
mark on card
OR
sprinkle iron filings
tap card
direction/alignment of iron filings show field
use compass/suspended small magnet to show direction
how to increase speed of motor
more turns/several coils
iron core
increase current
stronger magnet
smaller air gap
curved poles(if not in the diagram)
poles closer
use split ring commutator(if not used already)
emf. def.
energy supplied/work done per unit charge
to drive charge round a complete circuit
how to do induction
-ve induced:
+ve charge attracts electrons which are -ve
electrons move towards +ve charge
unbalanced +ve charges left at opposite end
