The variation of $EMF$ with time for four types of generators is shown in the figures. Which amongst them can be called $AC$?

Both alternating current and direct current are measured in amperes. But how is the ampere defined for an alternating current?

If ${E_0}$ represents the peak value of the voltage in an ac circuit,the r.m.s. value of the voltage will be

An alternating voltage is given by: $e = e_1 \sin \omega t + e_2 \cos \omega t$. Then the root mean square $(RMS)$ value of the voltage is given by:

The instantaneous voltages at three terminals marked $X, Y$ and $Z$ are given by
$V_x = V_0 \sin \omega t$
$V_y = V_0 \sin \left(\omega t + \frac{2 \pi}{3}\right)$
$V_z = V_0 \sin \left(\omega t + \frac{4 \pi}{3}\right)$
An ideal voltmeter is configured to read the $rms$ value of the potential difference between its terminals. It is connected between points $X$ and $Y$ and then between $Y$ and $Z$. The reading$(s)$ of the voltmeter will be:
$[A]$ $V_{XY}^{rms} = V_0 \sqrt{\frac{3}{2}}$
$[B]$ $V_{YZ}^{rms} = V_0 \sqrt{\frac{1}{2}}$
$[C]$ $V_{XY}^{rms} = V_0$
$[D]$ independent of the choice of the two terminals

In an $a.c.$ circuit,the instantaneous current and $emf$ are represented as $I = I_0 \sin(\omega t - \pi / 6)$ and $E = E_0 \sin(\omega t + \pi / 3)$ respectively. The voltage leads the current by