Question

In a wire AB, 25*10^21 electrons move from point A and B in 100 seconds. What is the current between A and B? What is the direction of this current?

Answer 1

Answer:

40 A, current is from B to A

Explanation:

The current in a wire is defined as:

$I=\frac{q}{t}$

where

q is the amount of charge passing a given point of the wire in a time interval t

The charge passing through a given point can be written as

$q=Ne$

where

N is the number of electrons

$e=1.6\cdot 10^{-19}C$ is the charge of one electron

So we can rewrite the equation as

$I=\frac{Ne}{t}$

In this problem:

$N=25\cdot 10^{21}$ is the number of electrons

t = 100 s is the time interval

Substituting, we find the current:

$I=\frac{(25\cdot 10^{21})(1.6\cdot 10^{-19})}{100}=40 A$

Moreover, the direction of a current is defined as the direction of positive charges moving. Here, the charge carriers are electrons (which are negatively charged), so the direction of the current is opposite to the direction of motion of the electrons: therefore, since the electrons move from A to B, the direction of the current is from B to A.