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6 Answers, Hints and Solutions 225
A5.3 See Fig. A.17.

(a) (b) 1.8

2.0 10 -12 d=100 nm 1.6
d=40 nm
d=20 nm 1.4
Drag force (N) 1.5 10 -12 Viscosity 1.0
1.2

0.8
-12
1.0 10
0.6
0.4
5.0 10 -13
0.2
0 20406080 100
10 100 1,000
Particle to wall distance (nm) Medium temperature T (C)
Fig. A.17. Drag force dependence on diameter of microsphere moving at constant
speed of v in water (a), and viscosity dependence on temperature of medium (b)

A5.4 See Fig. A.18.

10 -8
d=100 nm
d=40 nm
-10
10
van der Waals force (N) 10 -12 H=1.80 10 -20
d=20 nm

-14
10

10 -16

10 -18
1 10 100 1000
Distance (nm)
Fig. A.18. van der Waals force dependence on distance between particle and wall