Magnetism and EM Flashcards
How to make a magnet induced
an object made of a magnetic material
becomes a magnet when it is near or in contact with a magnet.
What constitutes a magnet
their magnetic domains are aligned
Stroking method
An unmagnetised steel bar is stroked several times from one end to the other, in one
direction, with one of the poles of a permanent magnet
Magnetisation by DC
The steel bar to be magnetised is placed inside a solenoid. A direct current is passed into
the solenoid to align the magnetic domains in a uniform direction.
Whats the direction of a magnetic field at a given pt
The direction of the field at a given point is defined as the direction of the force
that acts on a north magnetic pole placed at that point.
How to draw magnetic field lines using compass
Place a compass near a magnet and move it in the direction it points. Continue tracing the path and repeating this step til compass reach the other pole of the magnet
how can a ferrous core increase magnetic field
A ferrous core placed inside a current-carrying
solenoid is magnetised by the magnetic field.
The resultant magnetic field is the sum of the
field due to the current and that due to the
ferrous core
How can 2 parallel wires carry current in the same direction attract each other
wire Y would exert a magnetic force on X in the direction of F (to the right).
Likewise, by Newton’s Third Law, wire X would exert a force on Y towards the left.
How to increase turning effect of coil
(i) increasing the number of turns on the coil,
(ii) increasing the magnitude of the current,
(iii) using a stronger magnet, or
(iv) winding the coil onto a soft-iron cylinder.
What does the split ring commuator do
a split-ring commutator reverses the current in the coil
every half rotation when the coil is perpendicular to the magnetic field. This allows the coil
to continue to rotate in the same direction.
