A negatively-charged polythene strip is brought near the left end of an uncharged metal bar. This makes a plastic strip suspended near the right end of the metal bar move away from the metal bar. (a) How does the charged polythene strip affect the electrons in the metal bar? Explain your answer. (b)Why does the plastic strip move away from the right end of the uncharged metal bar?
When plastic strip is brought near the metal bar, the negative charge on the plastic strip induces (+) charge on the metal left face and to balance this, right face of metals develops a (-) charge. So when the plastic strip is brought near the left face, it is repelled due to repulsion of like charges.