## anonymous 4 years ago Two 10-cm-long thin glass rods uniformly charged to + 10\;{\rm nC} are placed side by side, 4.0 cm apart. What are the electric field strengths E_1, E_2, and E_3 at distances 1.0 cm, 2.0 cm, and 3.0 cm to the right of the rod on the left, along the line connecting the midpoints of the two rods?

1. anonymous

idk what my problem is. i know at 2cm E is 0. so to find E_1, i calculated by getting E at r=0.01 and subtracted r=.03

2. anonymous

i didn't think i would use the formula for infinite length rods since it's only 10cm

3. JamesJ

ok. Then you'll need this: http://online.cctt.org/physicslab/content/phyapc/lessonnotes/Efields/EchargedRods.asp

4. JamesJ

Now just plug away.

5. anonymous

i did!! i meant i used r^2=.01^2+.05^2. or am i suppose to use r=.01?

6. JamesJ

In your problem, L = 10 cm, a = 5 cm. Then what varies for each rod in each scenario is the perpendicular distance b.

7. anonymous

i did it just the way the formula is laid out and got 1.76*10^5 but the answer was 1.25*10^5...i think i see why it's 2 times charge density...