Question

shea rubs a silk cloth on a glass rod to create new charges in the materials. after doing this, he notices that the materials are attracted toward each other. the new charges in the two objects are shown as question marks (?) in the diagram. which of the following best describes the new charges of the particles in each material? glass rod: positive / silk cloth: positive glass rod: positive / silk cloth: negative glass rod: positive / silk cloth: neutral glass rod: negative / silk cloth: neutral

Explanation:

When a silk cloth is rubbed on a glass rod, the glass rod loses electrons (becomes positive) and the silk cloth gains those electrons (becomes negative). Opposite charges attract, so the glass rod (positive) and silk cloth (negative) are attracted. Let's analyze each option:

• Option 1: Two positive charges repel, so this is incorrect.
• Option 2: Positive and negative charges attract, which matches the observation and the charging by friction (glass loses electrons, silk gains) concept.
• Option 3: A positive and neutral object would have a weaker attraction (due to induction), but here charging by friction occurs, so silk isn't neutral. Incorrect.
• Option 4: Glass rod being negative and silk neutral doesn't fit charging by friction (glass should lose electrons/ be positive) and the attraction logic. Incorrect.

Answer:

B. glass rod: positive / silk cloth: negative