An electrometer consists of vertical metal bar at the top of which is attached a thin rod which gets deflected from the bar under the action of an electric charge (fig.) . The reading are taken on a quadrant graduated in degrees . The length of the rod is l and its mass is m . What will be the charge when the rod of such an electrometer is deflected through an angle α. Make the following assumptions :
(a) the charge on the electrometer is equally distributed between the bar & the rod
(b) the charges are concentrated at point A on the rod & at point B on the bar.