phil ess
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Homework Statement
You are 1.5m from a charge distribution whose size is much less than 1m. You measure an electric field strength of 282 N/C. You move to a distance of 2m, and the field strength becomes 119 N/C. What is the net charge of the distribution? HINT: Don't try to calculate the charge. Determine instead how the field decreases with distance, and from that infer the charge.
Homework Equations
E = kq/r2
The Attempt at a Solution
Well the electric field strength doesn't fall off as 1/r2, because if we calculate q for 1.5m using simple substitution, then use that q at 2m, I don't get the electric field given.
How do I figure out the field? If I am thinking graphically, I have two points (1.5,282) (2,119) and I have to find a curve that crosses those two points, a curve that describes how the electric field falls off.
I think the problem I am having here is that I am rusty on the math. I have a feeling that it would help to differentiate E = kq/r2 to perhaps be able to describe how the field is changing:
E' = -2kq/r3 But I am not sure how to use the given points to help...
E2/E1 = 0.422
r2/r1 = 4/3
Any hints would be appreciated!