Question

A positively charged insulating rod is brought close to an object that is suspended by a string. If the object is repelled away from the rod we can conclude: A) the object is positively charged B) the object is negatively charged C) the object is an insulator D) the object is a conductor E) none of the above Two small charged objects repel each other with a force F when separated by a distance d. If the charge on each object is reduced to one-fourth of its original value and the distance between them is reduced to d/2 the force becomes: A) F/16 B) F/8 C) F/4 D) F/2 E) F

Answer 1

Answer

A)   Positively charged two insulating rod are brought closed to an object  they repel each other. It means the Object is positively charged. Because similar charge repel each other.

   The correct answer is Option A.

B) we know force between to charges is calculated using Formula

         $F = \dfrac{kQ_1Q_2}{r^2}$.......(1)

   form the given condition in the question

          $F' = \dfrac{k\dfrac{Q_1}{4}\dfrac{Q_2}{4}}{(\dfrac{r}{2})^2}$

          $F' = \dfrac{k\dfrac{Q_1}{4}\dfrac{Q_2}{4}}{(\dfrac{r^2}{4})}$

          $F' = \dfrac{4}{16}\dfrac{kQ_1Q_2}{r^2}$

from equation (1)

          $F' = \dfrac{F}{4}$

hence, the correct answer is Option C.