46. The charge dq within a thin shell of thickness dr is ρ A dr where A = 4πr

2

. Thus, with ρ = b/r, we have

q =

dq = 4πb

r

2

r

1

r dr = 2πb

r

2

2

− r

2

1

.

With b = 3.0 µC/m

2

, r

2

= 0.06 m and r

1

= 0.04 m, we obtain q = 0.038 µC.