Electrical power transmission

1
Electrical power transmission This is carried out
at very high voltage and in a.c. For a given
power to be transmitted P VI In high voltage V
transmission, current flow I in cable is made
small. This reduces the power loss over the
connecting cables due to its resistance r as
dissipated heating is I2r. Under a.c. voltage,
the voltage value can be easily stepped up or
down for domestic use by transformers.
2
Electromagnetic braking When a metal is moving in
a magnetic field, eddy current is induced on it
and gives rises to heating effect. By Lenzs law,
the motion of the metal is damped by the effect
of induced current flow. (for example, the coil
in galvanometer is wound on an aluminium former.
As the coil rotates, induced current in former
damps the pointer motion to settle the pointer
position as quickly as possible.)
3
Induction heating If there is a changing magnetic
field around a metal piece, the induced current
on it will give rise to heating effect. (for
example, induction cooker) Magnetic levitation
The changing current in coils in train causes
induced current flow across coils installed along
the rails. By Lenzs law, repulsion force arises
between coils. The train is lifted up in air.