Mass of charged sphere suspended between charged plates

  • Thread starter krbs
  • Start date
  • #1
51
3

Homework Statement


A small sphere with charge 2.4 micro coulombs is suspended from a thread between 2 charged plates. The plates have a voltage of 62 and the distance between the plates is 3.1 cm. The sphere hangs at 18 degrees to the vertical.

Homework Equations


E = V/r
FE = Eq
Fnetx = FE - FT
Fnety = FTy - Fg

The Attempt at a Solution


[/B]
E = 62V/0.031m = 2000 N/C

FE = Eq = (2000 N/C)(2.3 x 10^-6 C)

FTx = FE = 4.6 x 10^-3 N

FTy = FE * tan18 degrees
= 4.6 x 10^-3 N * tan18
= 1.5 x 10^-3 N

Fg = mg
1.5 x 10^-3 N = m(9.8 m/s^2)
m = 1.5 x 10^-4 kg
 

Answers and Replies

  • #2
TSny
Homework Helper
Gold Member
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Hello. In the problem you state that the charge is 2.4 μC but you use 2.3 μC in the calculation.

You wrote FTy = FE * tan18o . Is this correct (keeping in mind that the 18o is measured from the vertical)?
 
  • #3
51
3
Hello. In the problem you state that the charge is 2.4 μC but you use 2.3 μC in the calculation.

You wrote FTy = FE * tan18o . Is this correct (keeping in mind that the 18o is measured from the vertical)?
I just realised the problem statement says 2.4 μC but the diagram says 2.3 μC hmmm. Assuming 2.4 is correct..

FTy = FE*tan72
= 1.5 * 10^-2 N

Fg = mg
1.5 * 10^-2 = m(9.8)
m = 1.5 ^ 10^-3 kg
 
  • #4
TSny
Homework Helper
Gold Member
12,963
3,320
That looks right.
 
  • #5
51
3

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