Đang chuẩn bị nút TẢI XUỐNG, xin hãy chờ
Tải xuống
Bộ tài liệu bài tập tham khảo môn vật lý bậc đại học bằng tiếng anh Chapter 25 | 25.1 Q It 3.6 A 3 3600 s 3.89 x 104 C. Q 420 C 2 25.2 a Current is given by I 80 60S 8.75 x 10 A. b 1 nqvdA I 8.75 x 10 2A V d nqA 5.8 x 1028 1.6 x 10 19 C n 1.3 x 10 3 m 2 1.78 x 10 6 ms. 25.3 . 4.85 A__ a Vd nqA 8.5 x 1028 1.6 x 10 19 C n 4 2.05 x 10 3 m 2 1.08 x 10 ms travel time 0 71m 6574 s 110 min vd 1.08 x 10 4 m s b If the diameter is now 4.12 mm the time can be calculated using the formula above or comparing the ratio of the areas and yields a time of 26542 s 442 min. c The drift velocity depends on the diameter of the wire as an inverse square relationship. 25.4 The cross-sectional area of the wire is A nr2 n 2.06 x 10 3 m 2 1.333 x 10 5 m2. The current density is J L -----800A - 6.00 x 105 Am2 A 1.333 x 10 5 m2 We have vd J ne Therefore J 6.00 x 105 A m2 -8 electrons n 519 6.94 x 1028 -- vde 5.40 x 10 5 m s 1.60 x 10 19 C electron m3 25.5 J nq vd so J vd is constant. Jd vd 1 J21 vd 2 vd2 vJJ1 vd1 ljl1 1.20 x 10 4 ms 6.00 1.20 6.00 x 10 4 ms 25.6 The atomic weight of copper is 63.55 g mole and its density is 8.96 g cm3. The number of copper atoms in 1.00 m3 is thus 8.96 g cm3 1.00 x 106 cm3 m3 6.023 x 1023 atoms mole 63.55 g mole 8.49 x 1028 atoms m3 Since there are the same number of free electrons m3 as there are atoms of copper m3 see Ex. 25.1 The number of free electrons per copper atom is one. 25.7 Consider 1 m3 of silver. density 10.5 x 103 kg m3 so m 10.5 x 103 kg M 107.868 x 10 3 kg mol so n m M 9.734 x 104 mol and N nNA 5.86 x 1028 atoms m3 If there is one free electron per m3 there are 5.86 x 1028 free electrons m3. This agrees with the value given in Exercise 25.2. 25.8 a Qtotal nCl nNa e 3.92 x 1016 2.68 x 1016 1.60 x 10 9 C 0.0106 C I Qo 0.0106 C 0.0106A 10.6 mA. t 1.00 s b Current flows by convention in the direction of positive charge. Thus current flows with Na toward the negative electrode. 8 8 x c . C . C o. 8 0 65 qi8 25.9 a Q I dt 55 -0.65 t2 dt 55t t3 329 C. Jv 7 I03I0 0 0 b The same charge would