Calculation of RMS current in half wave rectifier While calculating RMS current in half wave rectifier, why we will consider only half wave that means only we consider the limits 0 to pi. But here RMS current is for AC input..so why don't we consider and calculate as 0 to 2pi? Please clarify this. 
 A: We only consider the current from $0$ to $\pi$ since the current from $\pi$ to $2\pi$ is effectively 0. Consider a sinusoidal A.C. current $I = I_0\sin t$ (assuming the period is $2\pi$ as in your question), when there is a half wave rectifier, current can only flow in one direction. Thus any part of $I$ that is negative becomes zero. The current in the circuit becomes
$I =\begin{cases} 
      \hfill I_0\sin t    \hfill & 0 \leq t < \pi \\
      \hfill 0 \hfill & \pi \leq t < 2\pi \\
  \end{cases}.$
So it is the same to consider this function from $0$ to $2\pi$, or the original function from $0$ to $\pi$.
A: RMS means square mean root 
. i.e. take square add and take mean then take square root. If you take square of ac i.e. sinusoidal waveform the parts from $0$ to $\pi$ become identical to the part between $\pi$ to $2.\pi$. Hence if you add from $0$ to $n.\pi$ and divide by n you will essentially left with one lobe.
That's why you can only use one lobe to get the RMS value
I hope this will help. 
