Correct Answer - Option 2 : 5, √125 and √125
Concept:
PMMC measures dc or average value, hot-wire and moving iron instruments measures RMS value.
If a current i is given as:
i = a0 + a1 sin (ω1t + θ1) + a2 sin (ω2t + θ2) + a3 sin (ω3t + θ3) +...........
Where,
a0 = DC value = average value of current
Rms value is:
\(i_{rms}= \sqrt {a_0^2 + \frac{1}{2}\left( {a_1^2 + a_2^2 + a_3^2 + \ldots } \right)} \)
Calculation:
Given current i,
i = 5 + 14.14 sin (314 t + 45°)
PMMC meter reading = idc = average value = 5 A
Hot wire meter reading = Moving iron meter reading = irms
irms \( = \sqrt {{5^2} + \frac{1}{2}{{\left( {14.14} \right)}^2}} \) = √125 A.