# Physics help involving electric field charge

A proton orbits just at the surface of a charged sphere of radius 0.83 cm. If the speed of the proton is 4.96 X105 m/s, what is the charge on the sphere?

proton mass = 1.67e-27
proton charge = 1.6e-19

I thought maybe F = (mv²)/r
((1.67e-27)(4.96e5)²)/.0083

Then E=F/q

But this doesn't seem to be right.

Any help would be appreciated. I have tried it a couple times with no luck. Just need to get in the right direction. Thank you in advance!

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ehild
Homework Helper
What do you mean on E=F/q? What are E and q?

ehild

E = electric field
q = the charge
F = electric force

ehild
Homework Helper
You need the charge of the sphere. If E is the electric field strength at the place of the proton, the electric force on the proton is F=eE where e is the elementary charge. How are the electric force and the centripetal force related? How do you get the electric field of the sphere?

ehild

Thanks. I figured it out.