The process by which $ac$ is converted into $dc$ is known as
Purification
Amplification
Rectification
Current amplification
A resistance of $20$ ohms is connected to a source of an alternating potential $V = 220\,sin\,(100\,\pi t)$. The time taken by the current to change from its peak value to r.m.s value is
Two cables of copper are of equal lengths. One of them has a single wire of area of cross-section $A$, while other has $10$ wires of cross-sectional area $A / 10$ each. Give their suitability for transporting $A.C.$ and $D.C.$
The frequency of an alternating voltage is $50$ cycles/sec and its amplitude is $120\,V$. Then the $ r.m.s$. value of voltage is........$V$
The variation of $EMF$ with time for four types of generators are shown in the figures. Which amongst them can be called $AC$ ?
The voltage of an $ac$ supply varies with time $(t)$ as $V = 120\sin 100\,\pi \,t\cos 100\pi \,t.$ The maximum voltage and frequency respectively are