"Pumping" Charges — Question 2

Question 2

Electron transfer through a source has the same energy requirement as conventional pumping

Use $e=1.602176634\times10^{-19}$ C, exact. An ideal 9.00 V source moves $N=2.00\times10^{18}$ electrons internally from its positive terminal to its negative terminal in 5.00 s.

1. Find the conventional current direction and magnitude.

2. Find each electron potential-energy increase and the total non-electrostatic work.

Question 2 - Solution

Electron transfer through a source has the same energy requirement as conventional pumping

(a) Method and calculation

$$|Q|=Ne=.320435\,\mathrm C,\quad I=Ne/t=.0640871\,\mathrm A.$$$$\text{Conventional current inside source: negative terminal}\to\text{positive terminal}.$$

(b) Interpretation and further calculation

$$\Delta U_e=(-e)(V_--V_+)=9.00e=1.44196\times10^{-18}\,\mathrm J.$$$$W=N\Delta U_e=(Ne)(9.00)=2.88392\,\mathrm J.$$

Physical check

A negative charge increases its potential energy by moving to a lower electric potential.