Question

Rubbing a balloon causes it to become negatively charged. The balloon then tends to cling to the wall of a room. For this to happen, must the wall be positively charged?

Short answer

Explain. Answer: No, the wall does not have to be positively charged for the charged balloon to cling to it. When a negatively charged balloon is brought close to the wall, the induction effect causes a redistribution of charges on the wall's surface, creating an attractive force between the negatively charged balloon and the induced positive charges on the wall. This attractive force is enough to hold the balloon against the wall, even if the wall itself has no overall net charge.

Step-by-step solution

Understand the charge on the balloon

When a balloon is rubbed, it gains extra electrons from the other surface which causes it to become negatively charged. These negative charges (electrons) on the balloon create a small electrostatic force.

Explain the induction effect

When the negatively charged balloon is brought close to the wall, it induces a redistribution of charges on the wall's surface, even if the wall itself doesn't have any overall net charge. This is known as the induction effect.

Describe the redistribution of charges on the wall

As the negatively charged balloon is brought near the wall, its electrons repel the electrons in the wall, causing them to move away from the surface. Consequently, this leaves the surface of the wall with more positive charges (protons) closer to the balloon. So, there is a region on the wall with a higher concentration of positive charges and this attracts the negatively charged balloon.

Conclude if the wall must be positively charged

The wall does not have to be positively charged for the balloon to cling to it. The induction effect causes a redistribution of charges on the wall's surface, creating an attractive force between the negatively charged balloon and the induced positive charges on the wall. This force is enough to hold the balloon against the wall, even if the wall itself has no overall net charge.