The electrostatic force on a small sphere of charge 0.4 µC due to another small sphere of charge –0.8 µC in the air is 0.2 N. (a) What is the distance between the two spheres? (b) What is the force on the second sphere due to the first?
(a) Electrostatic force on the first sphere, F=0.2N Charge on this sphere, q1=0.4μC=0.4×10−6C Charge on the second sphere, q2=−0.8μC=−0.8×10−6C Electrostatic force between the spheres is given by the relation, F=4πε0r2q1q2 And, 4πε01=9×109Nm2C−2 Where, ε0= Permittivity of free space r2=4πε0Fq1q2 =0.204×10−6×8×10−6×9×109 =144×10−4 r=144×10−4 =0.12m The distance between the two spheres is 0.12 m. (b) Equal and Opposite Force acts on the other sphere (By newton's Third Law). Hence 0.2 N attractive
