What happens to the change carrier density

Question

If the current carried by a conductor is doubled what happens to 

a)the charge carrier density 

b)the current density 

c)the electron drift velocity 

d)the average time interval between collisions 

Answer 1

I would agree with every part of the previous answer, except the first one.  The density of charge carriers is (in typical cases) determined by the material, and thus unaffected by changes in current.  The change in current just means the charges move faster.  The electric field lines applying a force to the charge carriers get more dense (denoting an increase in E field strength) but the charges do not get proportionally more dense with current.

 

Also, for the second answer, I would add the important assumption that the current is uniform and changes uniformly.

 

Answer 2

I = nqv_dA

 

where n is the charge/volume

 

q is the charge per carrier

 

v_d is the drift velocity of the charge carriers

 

A is the cross-sectional area of current flow

 

 

a) n doubles if I doubles.

 

 

b) J = I/A is the current density.  If I doubles, J doubles.

 

 

c) v_d doubles if I doubles

 

 

d)  The average time interval between collisions depends inversely on v_d.  If I doubles, v_d doubles, so the average time between collisions is halved.