Solving Electric Field Problems

[rhaylor]

I'm just getting started here and need a little help. Need a general method to figure problems like these:

If a drop of mass 1.1 X 10 ‾14 kg remains stationary in an electric field of 1.68 X 10 N/C:

(a) What is the charge of this oil drop?

(b) How many extra electrons are on this particular oil drop (given the presently-known charge of the electron)?

Any help is deeply appreciated.

rhaylor

 

[ehild]

If a drop of mass 1.1 X 10 ‾14 kg remains stationary in an electric field of 1.68 X 10 N/C:

Well... What forces act on that oil drop? It is here on the Earth and it has mass, so it can not avoid gravity. And it is in an electric field, and it has charge, although unknown yet, but is does not move so the forces must cancel each other...

ehild

 

[wais]

Hi rhaylor,

Solving electric field problems can seem daunting at first, but with a general method, it becomes much more manageable. Here are some steps you can follow:

1. Identify the known values and unknown value in the problem. In this case, we know the mass of the drop (1.1 x 10^-14 kg) and the electric field (1.68 x 10^3 N/C), and we need to find the charge and the number of electrons.

2. Recall the equation for electric force, which is F = qE, where q is the charge and E is the electric field. We can rearrange this equation to solve for q: q = F/E.

3. Plug in the known values into the equation and solve for q. In this case, q = (1.1 x 10^-14 kg)(1.68 x 10^3 N/C) = 1.848 x 10^-17 C.

4. To find the number of electrons, we can use the fact that one electron has a charge of 1.6 x 10^-19 C. So, the number of electrons on the oil drop would be 1.848 x 10^-17 C / 1.6 x 10^-19 C = 115.5 electrons.

I hope this helps! Remember to always identify the known and unknown values, use the relevant equations, and double check your units to make sure they cancel out correctly. Best of luck with your studies!