An example of friction that can establish a difference of potential is?

• A. Rubbing a rubber balloon against hair
• B. Rubbing a glass rod with a piece of silk
• C. Using a battery to charge an object
• D. None of the above

Answer: (B)

Rubbing a glass rod with a piece of silk is a classic example of frictional charging, where the process of rubbing generates a difference of electrical potential due to the transfer of electrons. When the glass rod is rubbed with silk, electrons are transferred from the silk to the glass. This results in the glass rod becoming positively charged while the silk carries a negative charge. This phenomenon demonstrates how friction can lead to the separation of charges and thus establish a potential difference.

Friction is a key element in this process because it provides the necessary energy to overcome the forces binding electrons to the material, allowing for their transfer. The interaction between different materials—in this case, glass and silk—determines the direction of electron flow and ultimately the sign of the charge that each object acquires.

In contrast, rubbing a rubber balloon against hair also generates static electricity through a similar mechanism; however, the most commonly illustrated and recognized educational example of this effect tends to focus on the glass and silk scenario. The use of a battery to charge an object involves a different principle, as batteries provide a steady source of voltage rather than relying on friction to create the potential difference.