Question

Two substances are identical except that the electron mean free time for substance A is twice the electron mean free time for substance B. If the same electric field exists in both substances the electron drift speed in A is:

Answer 1

Complete Question  

Two substances are identical except that the electron mean free time for substance A is twice the electron mean free time for substance B. If the same electric field exists in both substances the electron drift speed in A is:

Select one:

a. half that in B

b. four times that in B

c. twice that in B

d. the same as in B

e. one fourth that in B

Answer:

Option c is correct

Explanation:

From the question given

The electron mean free time substance for substance is $\tau_A = 2 \tau_B$

The electron mean free time substance for substance B is $\tau_B$

Generally the drift velocity for substance A is mathematically represented as

   $_A\vec v_{d} =-(\frac{e \tau_A}{m}) \vec E$

Generally the drift velocity for substance B is mathematically represented as

      $_B\vec v_{d} =-(\frac{e \tau_B}{m}) \vec E$

So

      $_A\vec v_{d} =-(\frac{e 2\tau_B}{m}) \vec E$

=>   $_A\vec v_{d} =2 _B\vec v_{d}$