Problems #8, 9 and 10 refer to the same wire. [5] #8 . An electrical current of

Question

Problems #8, 9 and 10 refer to the same wire. [5] #8 . An electrical current of 9.50 mA exists in a solid cylindrical wire whose diameter is 3.50 mm and length is 10.8 m. Calculate the magnitude of the current density in the wire. Answer: (a) 0.99 kA/m2. (b) 2.51 kA/m2, (c) 3.81 kA/m (d) 4.24 kA/m2 e)4.81 kA/m2. (f) [6] #9. The resistivity of the wire in problem #8 is 7.66 x 10.8 Determine the electrical conductivity Answer: (a) 1.04 x 10 (ohmm), (b 1.31 x 10 (ohmm)-. (c 1.77 x 10 (ohmm (d 1.92 x 10 (e) 2.77 x 10 (oh-m. (f (obm-m)1 [8] #10, what is the potential difference between the ends of the wire to cause the current in #8 above? Answer: (a) 0.82 mV. (b) 2.59 mV, (c) 5.02 mV. (d) 8.66 mV. (e 10.1 mV. (f) [6] #11. For the figure at the right E-150 V , R 38.6 f2, and C 1700 E. How long after switch S is closed unil the current in the circut is stable? Answer: (a) 121 mb) 215 ms, (c) 328 ms. (d) 462 ms (e) 558 ms. (f) [10] #12. Circle the TRUE statement(s): a) Magnetic field lines form closed loops. b) For a magnet, the field lines leave the north pole and enter the south pole. c) A magnetic field is produced by a moving electric charge. d) A stationary electric charge produces a magnetic field. e) Magnetic field lines will cross to form right angles or angles less than 89 degrees. [8] #13. For the circuit at the right C1-25.0 mf. C2-40.0 mF C3- 55.0 mF, C4-70.0 mF and C5--85.0 mF Determine the value of CAB Answer: (a) 143 mF, b) 167 mF (c) 190 mF. (d) 250 mF (e) 286 mF. (f

Explanation / Answer

8) Current density J = I / A where A - Area, I - current

J = 9.50e-3 / pi*(1.75e-3)2

J = 0.987 kA/m2 ----- option (a) seems correct.

6) Electrical conductivity is is the reciprocal of electrical resistivity ()

= 1 / 7.66e-8 = 1.305e7 (ohm.m)-1 ----- option (b) seems fine

7) R = *L / A = 7.66e-8*10.8 / 9.621E-6

R = 0.08698.

Therefore, V = I*R = 9.50E-3*0.08698 = 0.816 mV ----- option (a) is correct.

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