A resistance of 20Ω is connected to a source of an alternating potential V=220sin(100πt) . The time taken by the current to change from the peak value to rms value, is

Both B and I are in the same phase. So, let us calculate the time taken by the voltage to change from peak value of rms value.Now, 220=220sin100πt1 .Or 100πt1=π2 or t1=1200sAgain, 2002=200sin100πt2 or12=sin100πt2o r 100πt2=π4Or t2=1400sRequired time =t1−t2=1200−1400=2−1400=1400s=2.5×10−3s