Physics

Problem

A conductor of cross-sectional area,

A

, is made from a material that has

n

free electrons per unit volume (

n

would be called the free electron number density). When a current,

I

, flows, the speed at which the free electrons move in the same direction is

v

. a. In 1 s, how far will each free electron move? b. In 1 s, how many free electrons will pass any point along the conductor. c. If each free electron carries a charge of

e

, how much charge passes any given point along the conductor in 1 s? d. Hence, show that the current,

I

, flowing in the conductor can be written as

I = nAve

. e. A conductor of cross-sectional area

1 \text{ mm}^2

is made from a material with a free electron number density of

1.0 \times 10^{29} \text{ m}^{-3}

. It is carrying a current of 100 mA. - i Calculate the speed at which the free electrons are moving. (The charge on an electron is

-1.6 \times 10^{-19} \text{ C.}

) - ii Comment on your answer to part i.

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