Electric Charge — Question 2

Question 2

The direction of electron transfer fixes the sign of charging

Two initially neutral objects A and B are rubbed together. Electrons carrying total charge $-3.20$ nC move from A to B; nuclei remain in their original objects and no charge leaves the pair. Later, electrons carrying $-.80$ nC move back from B to A.

1. Find both net charges after each transfer, using signed charge changes.

2. Find the net negative charge transported from A to B over the two stages and explain why positive charging does not require protons to move.

Question 2 - Solution

The direction of electron transfer fixes the sign of charging

(a) Method and calculation

$$\Delta Q_A=-(-3.20)=+3.20\,\mathrm{nC},\quad\Delta Q_B=-3.20\,\mathrm{nC}.$$$$Q_{A,f}=3.20-.80=+2.40\,\mathrm{nC},\quad Q_{B,f}=-3.20+.80=-2.40\,\mathrm{nC}.$$

(b) Interpretation and further calculation

$$Q_{\mathrm{transported}}=-3.20+.80=-2.40\,\mathrm{nC}.$$$$Q_A+Q_B=0\quad\text{at each stage}.$$Removing electrons leaves an uncompensated positive charge in A. No transfer of positively charged nuclei is needed.

Physical check

A transfer arrow specifies particle motion; its direction is not the sign of the transported charge.