# Linear/Surface/Volume Charge Density

1. Jan 18, 2009

### wbluem88

1. The problem statement, all variables and given/known data

(a) A charge of -345e is uniformly distributed along a circular arc of radius 4.00 cm, which subtends an angle of 41°. What is the linear charge density along the arc?

(b) A charge of -345e is uniformly distributed over one face of a circular disk of radius 1.90 cm. What is the surface charge density over that face?

(c) A charge of -345e is uniformly distributed over the surface of a sphere of radius 1.90 cm. What is the surface charge density over that surface?

(d) A charge of -345e is uniformly spread through the volume of a sphere of radius 1.90 cm. What is the volume charge density in that sphere?

2. Relevant equations

3. The attempt at a solution

OK so this should be really simple right??

Part a)

CHARGE / DISTANCE
(-345 * 1.602 * 10^-19)/((41/360)*2*pi*.04) = -1.9309*10^-15 C/m

Part b)

CHARGE / AREA
(-345 * 1.602 * 10^-19)/(pi*.019^2) = -4.8733*10^-14 C/m^2

part c)

CHARGE / AREA
(-345 * 1.602 * 10^-19)/(4*pi*.019^2) = -1.2183*10^-14 C/m^2

part d)

CHARGE / VOLUME
(-345 * 1.602 * 10^-19)/((4/3)*pi*.019^3) = -1.9236*10^-12 C/m^3

According to my WebAssign homework, all these are wrong. What am I doing?

2. Jan 18, 2009

### Dick

Nothing that I can see. I get a different exponent for the first one, but that's probably just a typo. Wrong number of significant figures? Something nit-picky like that?