3a: You have a rectangular solid. You would like to pass current through it so t

Question

3a: You have a rectangular solid. You would like to pass current through it so that it has the least resistance. Should you direct the current perpendicular to side A, B, or C? Explain. b: In a different experiment, current is passed through side A (and out the opposite side Use 0.2 m x 0.1 m x 0.02 m for the dimensions of the solid and assume that the solid is made of copper so its resistivity is p F 1.69 x 10 82m and n 8.49 x 102 e m3. The potential difference across the solid is maintained at 0.001 V. Determine the drift velocity of the elec- trons and then how long it would take a single electron to pass completely through the copper

Explanation / Answer

Given

   rectangular rod

a) we know that resistance , is directly proportional to the lenght of the conductor as lenght increases the resistance also increase so

to direct the current with least resistance , then the direction is perpendicular to side B aonly other sides has larger length than B.

b)

   from Ohm's law V = I*R ==> I = V/R

and relation between resistance and resistivity R = rhO*l/A

   and the formula for drift speed is Vd= J/ne = I/(neA)

   using I from ohms law Vd = V/(rho*l*n*e)

   substituting the values

               Vd = 0.001/(1.69*10^-8*0.1*8.49*10^28*1.6*10^-19) m/s

               Vd = 4.35*10^-5 m/s

nwo the time taken is t = x/v = 0.1/(4.35*10^-5) s = 2298.850 s

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