Hi friends in this video we are going to
see how to measure a power and the
equipment required for that is a vat
meter so we will see vat meter
connections also
so power is measured in AC circuit with
the help of vat meter
so lets discuss how to measure a power
using a vat meter for that I should
know vat meter connections so VAT meter has
a current coil to sense a current and a
voltage coil or pressure coil to sense
voltage so vat  meter has a box look like
this
so outside the box this particular
equipment having terminals M L C and V M
stands for mains L stands for load C
stands for common and V stands for
voltage and it is having current coil
and voltage coil or pressure coil
Function of current coil is to sense
current and function of voltage coil is
to sense voltage now current coil acts
like a ammeter and ammeter has very
low resistance in series with a
galvanometer so that make sense
that current coil should have very very
low resistance in order to have a very
low resistance this coil is made up of
thick wire with less number of turns so
it is just using expression R equal to Row
L by A so I am increasing the area and I
am decreasing the length by having less
number of turns in order to have low
resistance whereas voltage coil is like
a voltmeter having very high resistance
in parallel with a galvanometer so very
high resistance you will get if I have
more number of tons of thin wires so
this wire is thin area of cross section
is very low compared to the current coil
and
for number of turns are warmed so that
resistance is more so basically from the
VAT meter how we are getting a power so
the expression over here is simple power
is nothing but V into I where V is
nothing but the voltage sense by voltage
coil I is nothing but current sense by
current coil multiplied by cos of angle
between V and I so the current coil
current voltage coil voltage and
cosine of angle between these two
quantities will give you vat meter
reading that is nothing but power
consumed by a circuit thank you
