Radius of a Raindrop given Charge and Electric Potential

AI Thread Summary
A spherical raindrop with a charge of 5×10-6 C and a potential of 8.800×10-8 V is being analyzed to find its radius. The equation used is V = (kQ)/r, but the calculated radius is excessively large at 5.11*10^11 meters. Participants in the discussion suspect that the potential value might be incorrect, as it seems unusually low for the given charge. There is a consensus that the problem statement likely contains a misprint regarding the potential or charge values. Clarification of the problem's parameters is necessary to proceed accurately.
freddy13
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Homework Statement


A spherical rain drop carries a charge of 5×10-6 C and has a potential of 8.800×10-8 V at the surface. Find the radius of the drop.


Homework Equations



V = (kQ)/r

The Attempt at a Solution



I simply moved V and r to their respective spots and plugged in my numbers. I got a very large number of 5.11*10^11, so i am wondering if my units are wrong or if I am doing something else wrong. Thanks for your help!
 
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Hello, freddy13.

You're right, you're getting a ridiculous answer even though your method is correct. (Your answer for the radius is more than 3 times the distance to the sun.) The value for the potential looks very suspicious. Are you sure that 10 is raised to the negative 8 power? Also, the value for the charge seems very high for a raindrop.
 
Last edited:
Yeah I copied the problem exactly! It has to be something with the units that I am missing, that seems to be the only possibility!
 
I agree. It must be a misprint in the statement of the problem.
 
Thread 'Variable mass system : water sprayed into a moving container'

Thread 'Variable mass system : water sprayed into a moving container'

Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
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