What Speed Must an Electron Achieve to Orbit a Charged Sphere?

AI Thread Summary
To determine the speed an electron must achieve to orbit a charged glass sphere, the relevant equations involve the electric field and centripetal force. The electric field is calculated using the formula E = k*Q/(r^2), where r is the distance from the center of the sphere, which includes both the radius of the sphere and the additional distance above its surface. The relationship between the electric force and centripetal force is given by q*E = M*v^2/r. The main confusion arises from correctly defining the radius in these equations, as it should be the sum of the sphere's radius and the height above its surface. Clarifying this radius is essential for solving the problem accurately.
dtesselstrom
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Homework Statement


A 2.40 -mm-diameter glass sphere has a charge of + 1.70 nC.
What speed does an electron need to orbit the sphere 1.40 mm above the surface?

Homework Equations


Electric Field of Sphere: E=k*Q/(r^2)
q*E=M*v^2/r


The Attempt at a Solution


It seems pretty straight forward but I must be doing something wrong with the r values. Could someone tell me what the radius is considered. For the electric field is it the radius of sphere + the distance away or what and same for the other equation. I've tried pretty much all the combos I can think of and still am getting it wrong so not sure where I am going wrong.
 
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It says above the surface so you would have to add the radius of the sphere to the radius of the orbit.
 
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