Why is $220 \ V$ $AC$ more dangerous than $220 \ V$ $DC$?

What is the $r.m.s.$ value of an alternating current which,when passed through a resistor,produces heat that is thrice the heat produced by a direct current of $2 \ A$ in the same resistor (in $A$)?

Find the $RMS$ value for the saw-tooth voltage of peak value $V_0$ from $t = 0$ to $t = 2T$ as shown in the figure.

An alternating current is given by the equation $i = i_1 \cos \omega t + i_2 \sin \omega t$. The r.m.s. current is given by

$A$ resistance of $20 \Omega$ is connected to a source of an alternating potential $V = 200 \sin (10 \pi t)$. If $t$ is the time taken by the current to change from the peak value to rms value,then $t$ is (in seconds).

The instantaneous value of current in an $A.C.$ circuit is $I = 3 \sin \left(50 \pi t + \frac{\pi}{4}\right) \text{ A}$. The current will be maximum for the first time at