Question

1. find current when 100 million electrons flow through a cross section of a conductor in one micro second.
2. how much work is done in moving a charge of 5 C from infinity to a 5 A , if potential at A is 20 volt?

Answer 1

1. find current when 100 million electrons flow through a cross section of a conductor in one micro second.

2. how much work is done in moving a charge of $5\mathrm{C}$ from infinity to a $5\mathrm{A}$, if potential at A is 20 volt?

Solution

1. We use the formula for current:

$$I = \frac {\Delta q}{\Delta t} = \frac {N e}{\Delta t} = \frac {1 0 0 * 1 0 ^ {6} * 1 . 6 * 1 0 ^ {- 1 9}}{1 0 ^ {- 6}} = 1. 6 * 1 0 ^ {- 5} A = 1 6 \mu A$$

where $\Delta q$ - is charge that passed through a cross section of a conductor, $\Delta t$ - is time interval, $N$ - the number of electrons, $e$ - is charge of one electron.

2. The work is done in moving a charge A:

$$A = q \left(V _ {A} - V _ {\infty}\right) = 5 * (2 0 - 0) = 1 0 0 J$$

where $q$ is a charge, $V_{A}$ is a potential at the point $A$, $V_{\infty}$ is a potential at infinity.

Answer: 1) $16\mu A$; 2) $100J$.