Question

how can we find that the charged object is positively charged or negatively charged?

Answer 1

Compare with known positive / negative charge . find some material which you know takes up or gives away electrons . bring it close to the object in question . if they are of like charge , they will come together , otherwise they will repel

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Answer 2

There are two types of electrically charged objects - those that contain more protons than electrons and are said to be positively charged and those that contain less protons than electrons and are said to be negatively charged.

These two types of electrical charges - positive and negative - are said to be opposite types of charge. And consistent with our fundamental principle of charge interaction, a positively charged object will attract a negatively charged object.
Oppositely charged objects will exert an attractive influence upon each other. In contrast to the attractive force between two objects with opposite charges, two objects that are of like charge will repel each other. That is, a positively charged object will exert a repulsive force upon a second positively charged object. This repulsive force will push the two objects apart. Similarly, a negatively charged object will exert a repulsive force upon a second negatively charged object. Objects with like charge repel each other.