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Old Sep 7th 2009, 03:39 PM   #1
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Charged mass in electric field


As shown in the figure above, a ball with a mass of 0.180 g and positive charge of q=36.0 μC is suspended on a string of negligible mass in a uniform electric field. We observe that the ball hangs at an angle of θ=18.0o from the vertical. What is the magnitude of the electric field?


F=Mass*Gravity

Convert to Coulombs first.

Find the force of gravity on the object (Y
direction),F=Mass*Gravity. Then determine the x component of
using Force of gravity*TAN(Angle Given)

Divide by Coulombs.

based on those thoughts, I get .18*9.81 = 1.76580

next i take 1.77 * tan(18) = .57374

then i divided .57511/36E-6 = 15937.311

but its not the right answer =\
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Old Sep 7th 2009, 04:10 PM   #2
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$\displaystyle F_g = mg $

$\displaystyle F_c = Eq$

$\displaystyle \tan \theta = \frac {F_c}{F_g}$
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Old Sep 7th 2009, 05:52 PM   #3
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umm that still gives me the same answer...assuming I am solving for E which is still wrong =\

i got 15937.326 however the numbers after the decimals dont really matter in this problem
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