What is the potential difference across the capacitor?

AI Thread Summary
The discussion focuses on calculating the potential difference across a parallel-plate capacitor with specified dimensions and charge. The relevant equations include capacitance (C = Q/V) and the formula for capacitance in terms of physical parameters (C = epsilon * A/d). The user has calculated the area of the plates and the separation distance but is struggling with the final calculation, having tried several incorrect values. Another participant mentions having similar issues but eventually resolves their calculation errors. The thread emphasizes the importance of showing detailed calculations for clarity and accuracy.
Netsurfer733
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Homework Statement



"Two 2.1cm x 2.1cm plates that form a parallel-plate capacitor are charged to +- 0.705 nC. What is the potential difference across the capacitor if the spacing between the plates is 1.20mm? "

Homework Equations



C = Q/V

C = epsilon * A/d

The Attempt at a Solution



I figure epsilon = 8.85 x 10^-12 F/m
A = area of plates = 0.021 * 0.021 m^2
d = separation of plates = 1.2 x 10^-3 m

And so I've tried plugging it all in and I still didn't get it right. In my attempts, I've tried answering with 2.17, 3.25*10^-12 , and 2.16*10^11 with no luck. Can anyone point out where I've gone wrong?
 
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Have you calculated the potential difference or just tried numbers in random? Show your calculations in detail.

ehild
 
I did - but I apparently suffered a flurry of math errors. I got it anyway :)
 
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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