Question

how can we test that a object ,when it is rubbed get positive charge or nagative charge

Answer 1

By pacing the positive charge to it if is positive then it will repel if it is negative then it will attract ok

Answer 2

When you rub two different materials together, the friction between them produces a positive charge in one and a negative charge in the other. To determine whether one of them has a positive or negative charge, you can refer to a triboelectric series, which is a list of known materials sorted by increasing negative charge. Rubber, for example, is lower on the list than wool, so stroking rubber with wool will reliably create a negative charge in the rubber. Knowing this, and armed with an electroscope for measuring charge, you can determine whether the charge of an object is positive or negative.