Companion to the reading passage The Electrician of Philadelphia: How Benjamin Franklin Gave Electricity Its Language. Answer each question, then click Check. Multiple-choice and number questions grade themselves; for written answers, compare yours with the model answer and checklist, then score yourself honestly.
In the 1740s, Benjamin Franklin introduced the terms “positive” and “negative” charge that we still use today. A modern laser printer depends on those same charges. Inside the printer, a rotating drum is given a charge, and a laser marks the shape of the text on the drum. Tiny plastic toner particles are given a negative charge, so they stick to the marked areas. A roller then gives the paper a positive charge, creating an electric field between the drum and the paper. The electric field pulls the toner off the drum and onto the paper, where heat melts it in place. Engineers tested one type of toner. Their measurements are shown in Table 1.
Table 1: Properties of One Toner Particle
| Property | Value |
|---|---|
| Charge | −3.2 × 10−15 C |
| Mass | 6.0 × 10−13 kg |
| Diameter | 1.0 × 10−5 m |
| Electric field strength between drum and paper | 2.0 × 106 N/C |
Data are representative values for practice.
1. Which row correctly describes how toner is moved onto the paper? (Charge on toner / Charge on paper / Electric force on toner)
2. A printer engineer makes the following claim.
Place a check mark in either the Support or Refute box. Justify your response using a mathematical relationship.
Because every toner particle carries a negative charge, toner particles repel one another. This keeps the toner from clumping, so it spreads in an even layer. In one region of the drum, two toner particles, each with the charge given in Table 1, are 2.0 × 10−5 meter apart, center to center.
3. Substitute numerical values into a mathematical representation that can be used to determine the magnitude of the electric force between these two toner particles. Then calculate the force. (Enter the number in front of each power of ten.)
4. If the distance between the two toner particles doubled to 4.0 × 10−5 meter, the magnitude of the electric force between them would be
Charge that builds up on a person can jump to a doorknob or to a computer chip as a spark. Electronics workers worry about these sparks because a small discharge can damage a chip without anyone feeling it. Table 2 shows typical voltages that build up on a person during everyday activities in dry air and in humid air.
Diagram 1 (described in words): A student’s finger carrying a negative charge is brought close to the right side of a neutral, uncharged metal doorknob. The finger does not touch the doorknob.
Table 2: Typical Voltage Built Up on a Person
| Activity | Voltage at 10–20% Relative Humidity (V) | Voltage at 65–90% Relative Humidity (V) |
|---|---|---|
| Walking across a carpet | 35 000 | 1 500 |
| Walking across a vinyl floor | 12 000 | 250 |
| Worker moving at a workbench | 6 000 | 100 |
Data are representative values for practice.
5. Which statement best describes the pattern in the data in Table 2?
6. You are drawing the doorknob (a circle) with the negatively charged finger to its right, using + and − signs to show how charges are arranged on the neutral doorknob while the finger is near it. Place a check mark in three boxes to indicate features of a correct drawing.