Discussion
An energy-meter having a meter constant of 1200 revolutions per kWh is found to make 5 revolutions in 75 sec. The load power is _______.
Answer: C
The load power is 200 W.
At 1200 revolutions per kWh, 5 revolutions record 5/1200 kWh. Power is that energy divided by the time, 75 s.
\[ \begin{aligned} E &= \frac{5}{1200}\ \text{kWh} = \frac{5 \times 3.6 \times 10^{6}}{1200}\ \text{J} \\ &= 15\,000\ \text{J} \\ P &= \frac{15\,000}{75} = 200\ \text{W} \end{aligned} \]
The other options come from mishandling the hour-to-second conversion; a 1000 W load, for example, would turn the disc 25 times in 75 seconds.
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