P22_047.PDF

10 − 4 m 2 and

ρ is the charge per unit volume. The number of (excess) electrons in the rod (of length L =2 . 00 m) is

N = q/ (

−

e )where e is given in Eq. 22-14.

(a) In the case where ρ =

−

4 . 00

10 − 6 C/m 3 ,wehave

−

e = ρA

dx = |

N =

−

which yields N =2 . 00

10 10 .

(b) With ρ = bx 2 ( b =

−

2 . 00

10 − 6 C/m 5 )weobtain

N = bA

−

x 2 dx = |

AL 3

3 e

=1 . 33

10 10

47. The charge dq withinathinsectionoftherod(ofthickness dx )is ρAdx where A =4 . 00