A voltmeter having reading of 70 V on its 100 V range and an ammeter having reading of 80 mA on its 150 mA range are used to determine power dissipation in a resistor. Both these instruments are guaranteed to be accurate within $\pm 2 %$ at full scale deflection. The limiting error (in percentage) in power measuement is _______

6.6

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0.66

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2.857

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3.75

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Solution

The correct option is A 6.6
The magnitude of limiting error of the voltmeter
$= 0.02 \times 100 = 2 V$

Percentage limiting error at 70 V
$= \frac{2}{70} \times 100 = 2.857 %$

The magnitude of limiting error of the ammeter
$= 0.02 \times 150 m A = 3 m A$

Percentage limiting error at 80 mA
$= \frac{3}{80} \times 100 = 3.75 %$

$P = V I$

Percentage limiting error in power measurement
= 2.857% + 3.75%
= 6.607%

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