Oil Drop Electric Field Problem

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Homework Help Overview

The problem involves calculating the charge on a negatively charged oil drop given an electric field strength and distance. The subject area pertains to electrostatics and electric fields.

Discussion Character

  • Exploratory, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to apply the equation for electric field strength but expresses uncertainty about the correct manipulation to isolate charge. Some participants question the use of constants and their units, while others suggest verifying the dimensional consistency of the resulting expressions.

Discussion Status

The discussion is active, with participants providing feedback on the original poster's attempts and clarifying the importance of units in calculations. There is no explicit consensus on the correct approach yet, but guidance regarding the handling of constants and units has been offered.

Contextual Notes

Participants are navigating the implications of using the equation for electric fields and the significance of dimensional analysis in their calculations. There is a mention of a specific numerical answer, but the focus remains on the process rather than the outcome.

yasemonkey
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Homework Statement


An oil drop is charged negatively. How much charge is on the drop if the Electric Field is 6,400 N/C at a distance of 1.2 m?

Homework Equations


E=k q/r^2
I don't know if I should be using that equation for this one.

The Attempt at a Solution


I tried to do E/(k x r^2) = q but that didn't work
I also tried E/r^2= q but that also didn't work

I know the answer has to be 1.3 x 10^3

Thanks in advance for all the help!
 
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You have the correct equation for field strength, you are just not solving correctly for q.

A good check is whether or not your resulting expression has the correct physical units.
 
hmm... okay

and I'm right in saying k= 9 x 10^9
 
No. As many other constants, k is dimensionful and k = 9 x 10^9 N m^2/C^2 - units are important and the units of your final answer must also make sense.
 
Orodruin said:
No. As many other constants, k is dimensionful and k = 9 x 10^9 N m^2/C^2 - units are important and the units of your final answer must also make sense.
Oh I have to square root k x r^2 !
 

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