An atom of plutonium-239 has a nuclear radius 6.64fm and atomic number z=94. assuming that the positive charge is distributed uniformly within the nucleus, what are the magnitude and direction of electric field at the surface of nucleus due to the positive charge?

You could use Gauss law..

E.(4R²)=Ze/.

according to gauss law

E.dA=

E=(94*charge on electron)/4

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