As shown in figure (a), two identical metal balls supported by insulator stand are made to contact each other. Insulator stand is chosen so that charges induced in the metal sphere will not flow to ground. A glass rod rubbed with silk/woolen cloth is charged negatively. Such a negatively charged rod is brought very near to one of the metal ball as shown in figure(b). Due to force of repulsion, electrons will try to flow away from ball-A and will accumulate in the other side of ball-B. Now as shown in figure (c), let us separate the two balls. Excess electrons in the ball-B can not flow back to Ball-A, hence they are distributed uniformly on the surface of ball-B. Now let us remove the negatively charged glass rod as shown in figure(d). Excess positive charges cannot flow to ball-B, hence positive charges are distributed uniformly over the surface of Ball-A. Now we have two separate metal balls charged positively and negatively. This method of charging the metals is known as charging by induction.