Answer / gajanan

apperent power = voltage X current,
we can calculate apperent power by ammeter and voltmeter
reading but
real power = voltage X current X power factor

to measure real power we need wattmeter

Answer / nageshwaran.n

No doubt, we could use Voltmeter & Ammeter for calculating
Power but only Apparent Power that too at that instant.
Apparent power = voltage X current,

Actual RMS Power (real power) = voltage X current X power
factor

And to measure real power we need Wattmeter only.

Answer / smita

RIGHT POWER IS VOLTAGE X CURRENT BUT FROM THIS WE GET ONLY
APPERENT POWER,AND WE REQIRE REAL POWER I.E VOLTAGE X
CURRENT X POWE3R FACTOR AND FOR THAT WE REQUIRE WATTMETER

Answer / pillay

Yes as all have already said you dont need to use a watt meter
only if the circuit uses a Direct Current voltage and you can
calculate the power mentally by just looking at the voltmeter and ammeter.

Answer / sudheer

if we use more no of meters error is more

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