No.4

xx+dxx=0n A v ~10-20m2dx

vvdxx

x=00x

(a0=5.29x10-11m10-20m22

xx+dxmfp

1:

10-16s

before collisionafter collisionm1m1m2m2v1v2v1v2

before collisionafter collisionm1m1m2m2v1v2v1v2vr

or ()

()

Q dWAB

ABAB

before collisionafter collision

before collisionafter collisionm2m1m2

=(3/2)T1(m1)(m2) m2/m1 (m2/m1 > 1000)

(r0

90o x

90Coulomb logarithm10

From ChenlnL 10 n:D:

ldelectronionelectronelectron