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Asked in JEE Main 2010 · Non-uniform charge density
Enclosed charge inside radius r: q=∫₀^rρ₀(5/4-(r')/R)4π r'²dr'=4πρ₀[(5r³)/(12)-(r⁴)/(4R)].
Gauss's law: E(4π r²)=q/(ε₀), so the 4π cancels and E=(ρ₀)/(ε₀ r²)[(5r³)/(12)-(r⁴)/(4R)].
E=(ρ₀ r)/(ε₀)[5/(12)-r/(4R)].
Taking 1/4 out of the bracket: E=(ρ₀r)/(4ε₀)(5/3-r/R).
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