(II) An oil drop whose mass is 2.8 x 10-15 Kg is held at rest between two large plates separated by 1.0 cm (Fig. 27-3), when the potential difference between the plates is 340 V. How many excess electrons does this drop have?
Solution 3P: We have to calculate the number of electron possessed by an oil drop in Millikan’s oil drop experiment owing to which it remain suspended in between the air. Step 1 of 3 Concept: Weight of the oil drop is Fg= mg is directed directly downwards due to Earth’s gravitational force. Electric force acting on the charged oil drop is Fe= qE which is directed in the vertically upward direction. Here, q Charge on the oil drop E Electric field between the plates Electric field between the two parallel plates separated by the distance d when a potential difference of V is applied across it ends, is given as, E = V d