How Do You Calculate Capacitance and Electric Field for a Homemade Capacitor?

[mer584]

Homework Statement

A homemade capacitor is assembled by placing two 9inch pie pants 5cm apart and connecting them to the opposite terminals of a 9V battery. Estimate A) the capacitance, B) the charge on each plate c) the electric field halfway between the plates d) the work done by the battery to charge the plates.

Homework Equations

C=Eo(A/d) V=Ed Q=VC W= Q(V/2) PE= 1/2(QV)= 1/2(CV^2)= 1/2(Q^2/C)

The Attempt at a Solution

I was able to use the first formula I listed to solve for part A finding C= 7 x 10^ -12 and the third formula to solve for part Q= 7x 10^-11 but I can't seem to get part c. I tried using V=Ed but it doesn't give me the answer I'm looking for which should be 200 V/m.

 

[Doc Al]

What answer are you getting? (What if you round it off?)

 

[mer584]

I was getting 360 but then I realized that you probably want to divide the 9/2 since the voltage will be split evenly between each plate so then you end up getting 180..which may be close enough to 200??

 

[Doc Al]

I was getting 360 but then I realized that you probably want to divide the 9/2 since the voltage will be split evenly between each plate

Use the equation V = Ed to solve for E.

so then you end up getting 180..which may be close enough to 200??

That's what I'd say. 180 rounded to one significant figure is 200.