**Can someone check the answer below?** 26.70 A caterpiller of lenth 4.0 cm craw

Question

**Can someone check the answer below?**

26.70 A caterpiller of lenth 4.0 cm crawls in the direction of electron drift along a 5.2-mm-diameter bare copper wire that carries a uniform current of 12A.

a. What is the potential difference between the two ends of the caterpillar?

b. Is its tail positive or negative relative to its head?

c. How much time does the caterpillar take to crawl 1.0cm if it crawls at the drift speed of the electrons in the wire? (The number of charge carriers per unit volume is 8.49x1028 m-3.)

Explanation / Answer

Area of copper wire : Pi/d*d2 = 2.123x10-5 m2

lenght of catrepillar : L : 0.04 m

Resistivity of copper is: 1.69 x 10-8 ohm-meter

no. density of charge carriers in copper: ? = 8.49 x 10 28 m-3

(a) volatge V = iR = i?L/A

                 V = (12*1.69 * 10-8 * 4*10-2) /2.123x10-5

                    = 0.382 mV

(b) current i is opposite to electron drift

        i runs from Vhig to Vlow

        So, the head is at higher potential.

(c) Vd = drift velocity

      ?t = ?x / Vd

        Vd = J / ne = i / Ane

       ?t = ?x .Ane /i

             = 10-2 * 2.123x10-5 *8.49*1028 *1.602*10-19/ 12

             = 240.5 sec

time it takes to crawl is 240.5 sec

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