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

Answer: No, the wall does not have to be positively charged for a negatively charged balloon to cling to it. A neutral wall can still attract the negatively charged balloon due to the polarization effect, which causes a temporary charge redistribution within the wall's atoms, creating an attractive force between the balloon and the wall.

Step-by-step solution

Understanding Electric Charge

Electric charges exist in two types: positive and negative. Protons carry a positive charge, electrons carry a negative charge, and neutrons are neutral. When an object gains or loses electrons, it becomes charged. In the case of a balloon, it is becoming negatively charged because it is gaining extra electrons from rubbing against another material.

Understanding Electrostatic Force

When two charged objects are near each other, they experience an electrostatic force, which can attract or repel them. This force is described by Coulomb's Law: F = k * (|q1 * q2| / r^2), where F is the force, k is a constant, q1 and q2 are the charges of the objects, and r is the distance between them. If the charges have opposite signs (one positive and one negative), the force is attractive, and if the charges have the same signs, the force is repulsive.

The Charged Balloon Attracting Neutral Objects

While it is tempting to think that the wall must be positively charged for the balloon to cling to it, this is not necessarily the case. A negatively charged balloon can also be attracted to a neutral object, such as a wall. This phenomenon occurs due to the polarization effect, where the negative charge on the balloon causes a redistribution of charges within the wall's atoms, creating a localized region of positive and negative charges.

Understanding Polarization Effect

Polarization occurs when the negatively charged balloon induces a temporary charge separation in the wall, which is initially neutral. The negative charge on the balloon attracts the positive charges (protons) within the wall, while repelling the negative charges (electrons) away from the surface. This creates a region of positive charge close to the negatively charged balloon, which then attracts the balloon to the wall. This attraction is weaker than if the wall were actually positively charged, but it is still strong enough to make the balloon cling to the wall.

Conclusion

In conclusion, the wall does not need to be positively charged for a negatively charged balloon to cling to it. A neutral wall can still attract the negatively charged balloon due to the polarization effect, which causes a temporary charge redistribution within the wall's atoms, creating an attractive force between the balloon and the wall.