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Electricity and magnetism confusion! 
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#1
Dec2912, 09:28 AM

P: 20

1. The problem statement, all variables and given/known data
I've been set an assignment and I'm struggling with one question in particular: 2. Relevant equations 'Use the following data and plot the graphs for a point charge' 'Plot graph of E against r^2. Interpret the graph to describe electric field strength and electric potential.' The figures provided are r(m)=Distance from a point charge, and, V(V)=Voltage at a distance 'r' from a point charge. 3. The attempt at a solution More than anything I'm just really stuck how to find E from the figures provided? Any help would be greatly appreciated! Thanks 


#2
Dec2912, 09:37 AM

P: 123

The filed at r=r_{i} wil be:
E = dV/dr ≈ ΔV_{i}/Δr_{i} where ΔV = V(r_{i+1})V(r_{i}) and Δr_{i} = r_{i+1}r_{i} 


#3
Dec2912, 10:02 AM

Math
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Thanks
PF Gold
P: 39,557

I don't see how it would be possible to answer this without knowing what data you are given!



#4
Dec2912, 03:07 PM

P: 20

Electricity and magnetism confusion!
Apologies, the date given is as follows:
R(m)=Distance from point charge: 0.0254 0.0508 0.05762 0.1016 0.127 0.1524 0.1778 And corresponding respectively, the V(V)=VOltage at a distance 'r' from a point charge: 236.22 214.57 157.58 108.03 94.48 85.3 73.11 


#5
Dec2912, 03:31 PM

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P: 11,689

You're told that the given data corresponds to potential U at distances r from a point charge. What expressions do you know that correspond to electric potential U and electric field E at distance r from a point charge?



#6
Dec3012, 05:36 PM

P: 20

Ok, so from equations to give V and E, I've come up with this as a potential solution for the first E value from the first two values of distance and voltage. Is this correct?



#7
Dec3012, 07:41 PM

Mentor
P: 11,689

No need to plug in numerical values yet; you have a whole table full of values to plot later. Just write the expressions for potential and electric field for a point charge. Solve the potential expression for Q and substitute it into the field expression. That'll leave you with an expression for E involving only V and r. You can plot that since you have a table full of values for V and r.
(as an aside, note that electric field strengths are given in V/m or N/C, not Teslas which are a measure of magnetic field strength) 


#8
Dec3012, 08:35 PM

P: 20

Brilliant, piece of cake. Many thanks to those who have helped!



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