How can you charge a metal sphere positively without touching it ?

Explanation

Consider an isolated metallic sphere as shown in figure (a). Net charge on this sphere is zero.

Now, bring negatively charged rod quite close to above sphere as shown in figure (b). Because of this, free electrons in the sphere move away because of repulsion. As a result, part of surface of sphere nearer to rod becomes positive and part of surface of sphere, farther from rod becomes negative.
Now, make this farther part of surface of sphere grounded with the help of conducting wire, as shown in figure (c).
Now these accumulated electrons rush towards ground as shown in figure (d).
When we disconnect the sphere from the ground, positive charge on the sphere still remains attracted towards negatively charged rod.
Now when the rod is taken away, positive charge on the sphere gets distributed uniformly on its surface as shown in figure (e).
Such a method of charging in which electrically neutral body gets charged up by a charged body without any physical contact is called "charging by induction".
Note : In case of charging by induction, inducing charge and induced charge are opposite in nature. If the body to be charged is metallic these charges are of equal in magnitude.
Ground is negatively charged.