<p>In the a.c. circuit shown in Fig. 7.39, the main supply has constant voltage but variable frequency. For what frequency will the voltage across the resistance R be maximum?</p>

<p><img alt="" src="https://school.achievam.com/upload/questionbank/question/que_1758780515.png" style="height:120px; width:204px" />Fig 7.39</p>