Question

If through some cross-section of a conducting wire (lying along the x axis) 10 moles of electrons passes in 10 seconds in the positive x direction. What is the current through it ?
[$N_a$ here represents the Avogadro’s number, $6.022\times {10}^{23}$]

• A. e $N_a$ amperes in the positive x direction
• B. e $N_a$ amperes in the positive y direction
• C. e $N_a$ amperes in the negative x direction
• D. 10 e $N_a$ amperes in the negative x direction

Answer 1

The correct option is C e $N_a$ amperes in the negative x direction

It is very important to understand that 1 mole of electrons implies a total of $6.022\times {10}^{23}$ electrons. Now it is clearly given that 10 moles of electrons flow through the wire in 10 s.
Current, $I=\frac{Q}{t}$
And Q=ne=$10\times 6.022\times {10}^{23}\times e$, where e is the charge on each electron.
$I=10\times 6.022\times {10}^{23}\times \frac{e}{10}A$
$=6.022\times {10}^{23}\times e=e{N}_a$ Amperes.
And the direction of flow of electrons is opposite to the direction of current. So if the electrons are flowing in the positive x direction, current must be flowing in opposite i.e. negative x direction!