The resistivity of a semiconductor can be modified by adding different amounts o

Question

The resistivity of a semiconductor can be modified by adding different amounts of impurities. A rod of semiconducting material of length L and cross-sectional area A lies along the x-axis between

x = 0 and x = L. The material obeys Ohm's law, and its resistivity varies along the rod according to

?(x) = ?0exp(?x/L).

The end of the rod at is at a potential V0 greater than the end at x = L.(a) Find the total resistance of the rod and the current in the rod. (Use the following as necessary: ?0, V0, L, A, and x.)

(b) Find the electric-field magnitude E(x) in the rod as a function of x. (Use the following as necessary: ?0, V0, L, A, and x.)
E(x) =

(c) Find the electric potential V(x) in the rod as a function of x. (Use the following as necessary: ?0, V0, L, A, and x.)
V =

Explanation / Answer

We know that Resistance R= rho L/A

for current use I=V/R

B) Use gauss theorem for electric field

C) we know that E=dV/dr

Note: this is very good question can you please explain the meaning of text used in fourth line (?(x) = ?0exp(?x/L).)

the use of ? confused me.

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