Electricity: Static Electricity

Static Electricity: Audio Guided Solution

Problem 7:

It happened during Wednesday's physics lesson on charging by friction. A small white object began to slowly emerge from beneath the sleeve of Mr. H's sweater. It took several laughs and giggles from the class before the emerging sheet of fabric softener caught Mr. H's attention. He turned the potentially embarrassing moment into a serendipitous moment. Pulling the sheet out from beneath the sweater, Mr. H wrote the following problem on the board.

A sheet of cationic fabric softener having a surface charge of 3.6x10-12 C (positive) clings to a wool sweater with a negative charge of 6.8x10-9 C. Determine the force of electrical attraction if they can be treated as point objects with a separation distance of 0.019 cm.

What is the answer to this problem?

Habits of an Effective Problem Solver

• Read the problem carefully and develop a mental picture of the physical situation. If necessary, sketch a simple diagram of the physical situation to help you visualize it.
• Identify the known and unknown quantities; record them in an organized manner. A diagram is a great place to record such information. Equate given values to the symbols used to represent the corresponding quantity - e.g., Q1 = 2.4 μC; Q2 = 3.8 μC; d = 1.8 m; Felect = ???.
• Use physics formulas and conceptual reasoning to plot a strategy for solving for the unknown quantity.
• Identify the appropriate formula(s) to use.
• Perform substitutions and algebraic manipulations in order to solve for the unknown quantity.