# Physics: electric fields and positive charges

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1. In a radical system the electric potential is given by the function

V(r)=k(1/r2 - 1/r)

Where k is constant and r is the radical distance.

a. Find the electric field as a function of distance.

b. If a positive charge was released in this system, at what radius would it be at equilibrium (i.e. if electric potential was height and you rolled a ball on this landscape would it come to a rest?)

Take the derivative and put it equal to zero.

2. The earth has an electric field of 150N/C which arises because the separation of charge between the Earth's surface and the ionsphere which is 100 km above the surface of the earth. Assuming the Earth's atmosphere can be considered to be similar to a parallel plate capacitor (whose area is the area of the planet) what is the charge stored in this capacitor?

Treat the planet's atmosphere like a parallel plate capacitor. Use the parallel-plate capacitor equations.

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The solution discusses the electric fields and positive charges.