Concepts of Physics

IIT JEE Physics (1978-2018: 41 Years) Topic-wise Complete Solutions

Electrostatic attraction and repulsion with two balloons

Objective

To study the charge appearing on rubbing.

Introduction

When two objects are rubbed against each other, charge gets transferred from one to other. One of the objects becomes positively charged and other becomes negatively charged. The unlike charges attract each other and like charges repel. A charged body brought near an uncharged (neutral) body can cause redistribution of charges on the neutral body and two may attract each other.

Apparatus

Two balloons

Procedure

Repulsion

Take two balloons and blow air in them. Tie their ends with a string of about 10 cm length. Hold them in two hands and rub them few times against your hair. Hold the two through the strings and bring the rubbed part closer. The repulsion is clearly seen. Now, keep one of the balloon on the table and hold the other in your hand. Bring it close to one on the table and play with repulsion. You can make the balloons to go in circles on the table.

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Attraction by induction

Bring a charged balloon close to some pieces of paper. The pieces of paper jump and get stuck to the balloon. This phenomenon is generally described in all science textbooks at the middle level by using a comb. But experience is that the balloon can lift much larger pieces of paper and demonstration becomes much more impressive.

Discussion

Rubbing produces electrically charged objects. Emphasize that charge has not been created, it is only transferred. When the balloon is brought close to the paper pieces, it attract the pieces even though pieces are uncharged. The attraction is caused by the charge induced in the pieces of paper when they are brought close to the charged balloon.