Question

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 _______

• A. 6.6
• B. 0.66
• C. 2.857
• D. 3.75

Answer 1

The correct option is A 6.6

The magnitude of limiting error of the voltmeter
$=0.02\times 100=2V$

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

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

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

$P=VI$

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