Irodov – Problems in General Physics

3.205. (a) I = (V 0IR) e-2tIRC-

'

(b) Q = 1 /4
3.206. elm = lcor/qR = 1.8.10 11 C/kg.
3.207. p = lImle = 0.40 RN • s.
3.208. s = enl (v)11, 7 m, where n is the concentration of 10
free electrons, (v) is the mean velocity of thermal motion of an
electron.
3.209. (a) t = en1SII = 3 Ms; (b) F = enlpl = 1.0 MN,
where p is the resistivity of copper.
3.210. E (I12:-ce 0 r) ym/2eV=32 V/m, 6,9=(//4neo) V m/2eV =
= 0.80 V.
3.211. (a) p (x)= — 419 E 0 ex-2 13 ; (b) j =^4 /^9 E,a^3 /^2 V 2e/m.
3.212. n = Idle (u:^ ii-(;) VS = 2.3.10^8 cm-3.
3.213. uo = (1) 0 / 2 /2Vo.

3.214. (a) ni = I satIeV = 6.10 9 cm--3 .s -1; (b) n = V nilr

6.10 cm 7 -3.

3.215. t= 1)/ V rn = 13 ms. i

3.216. t = EAU/enid 2 = 4.6 days.

3.217. I = evaead.

3.218. j = (ecui — 1) enila.

3.219. (a) B = μ,I/2R = 6.3 p.T; (b) B = 1A^0 R^2 I12(11^2 x^2 )^312 =

= 2.3 RT.

3.220. B = ntio/ tan (n/n)/2nR, for n^ oo B = I.1^0 //2R

3.221. B = 414l/ltd sin 9 = 0.10 mT.

3.222. B = (n — 9 tan 9) Ro//2nR = 28ta.

3.223. (a) B = P 4 ' 91. ( 2n: (1) + b) ) ; (b) B = 43 .t 1 ( 4 : +.17b 2.

3.224. B R oh//1-t^2 Rr, where r is the distance from the cut.

3.225. B = RoIln 2 R.

3.226. (a) B = (p, 0 /4n) (nER); (b) B = (p, 0 /41t) (1 + 3n/2) PR;

(c) B = (p, 0 /411) (2 n) IIR.

3.227. B= (11 0 /4n)1y 2/i = 2.01LT.

3.228. (a) B = (11 0 /4n) V4 -I- n 2 I1R = 0.30 RT; (b) B = (p. 0 /4n) X

x 1/2 +2n + n 2 PR= 0.34p,T; (c) B = (p.^0 /4n) V 21/R= P.11 ELT.

3.229. (a) B = Ni/2; (b) B = Rot between the planes and

B = 0 outside the planes.

3.230. B=

ttoix inside the plate,

Roid outside the plate.

3.231. In the half-space with the straight wire, B = p,o//2nr,

r is the distance from the wire. In the other half-space B = 0.

3.232. The given integral is equal to Rol.

3.233. B

1 / 2 u0 [Jr] for r-<„,11,

1 /^2 p,o [jr] R^2 /rz for

3.234. B = 1 / 2 p. 0 UM i.e. field inside the cavity is uniform.

3.235. j (r) = (b I p, 0 ) (1 a)