Q 1.2) 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 = 0.2 N
Charge on this sphere, q1=0.4μC=0.4×106C
Charge on the second sphere, q2=0.8μC=0.8×106C
The electrostatic force between the spheres is given by the relation
F=14πε0q1q2r2
Where, ε0 = Permittivity of free space and 14πε0=9×109Nm2C2
Therefore.

r2=14πε0q1q2F

=0.4×106×8×106×9×1090.2=144×104r=144×104=12×102=0.12mThe distance between the two spheres is 0.12 m.

(b) Both the spheres attract each other with the same force. Therefore, the force on the second sphere due to the first is 0.2 N.