Question

To test if a body is charged or not you will use
a. Another uncharged body
b. A positively charged body
c. A negatively charged body
d. A positively and negatively charged body

and why?

Answer 1

Option d is correct

The only way to tell if a body is charged is to place a known positively charged body near it and later a known negatively charged body near it. If either charged body repels the object being tested, then the object is charged, and not just polarized.

A charged body will always create a polarization of charges on a neutral body, and so the second body will appear to be charged too, and be attracted to the first.

By "polarization" I mean the way electrons will move around so that, if the nearby charged object is positively charged, the electrons in the neutral object near it will be drawn to the side nearest the positively charged object. And if the charged object is negative, the electrons of the neutral object will be driven away from the side nearest the charged object.

The net result will thus be that the resulting charge on the neutral object will split, so that the side nearest the charged object will always carry an opposite charge and the side away will carry the like charge.

The only time you can get repulsion is when there is an actual imbalance of charges in an object that is strong enough not to be overcome by a polarizing effect.