The diameter of a 12-gauge copper wire is 0.081 in. the maximum safe current it can carry (in order to prevent fire danger in building construction) is 20 a. at this current, what is the drift velocity of the electrons? the number of electron carriers in 1.0 cm3 of copper is 8.5 × 1022 and e = 1.60 × 10-19 c.

Explanation:

v = I / (n q A)

where A is the cross sectional area (you are given diameter, so A = (pi/4) * d^2), n is the number of charge carriers in a volume, and q is the charge of each carrier (-1.60x10^-19). I is the current, in Amps.  

You will need to either convert your diameter from inches to centimeters or you will need to convert your volume in cc to cubic inches. I'd convert diameter.

the skeletons of most mammals reach a certain size and then stop growing. however, many animals, including some mammals, keep growing throughout their lives. kangaroos, for example, just keep growing and growing until they die. also, the longer an animal lives the greater the chance it might catch some deadly disease.