30. The surface charge density of a spherical charged sheet is 1 C/m2. If the radius of the circular sheet is 10 cm, calculate the electric field at a point 20cm away from it. 1 ads Hint: E = Jds= 0 4R2 2 48 or -x4x3.14x(01)2 1 10-6 9 10 X X (0.20) =2.826 x 10 N/C Ans. 2.83 x 10 N/C 31. Determine the intensity of electric field which can balance a drop of oil of mass 0.001 mg carrying 3 electronic charge. (UP 2019) Hint: Given, mass of a drop of oil =0.001 mg=10 kg And, electronic charge on the drop of oil = 3e = 3 x 16 x 10-19 C = 4.8 10-19 C The intensity of electric field, E= F 9 mg = (F=mg) 10-9 9.8 = x =2.04 1010 N/C 4.8 10-19