How Do You Calculate the Capacitance of a Homemade Capacitor?

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Homework Help Overview

The discussion revolves around calculating the capacitance of a homemade capacitor constructed from aluminum foil and paper. The original poster provides dimensions and the dielectric constant, seeking assistance with the capacitance formula.

Discussion Character

  • Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants discuss the correct application of the capacitance formula, questioning whether the area or length of the plates should be used. There is confusion regarding unit conversions and the dimensions provided.

Discussion Status

Some participants have offered guidance on ensuring the area is calculated correctly and emphasized the importance of using consistent units. There is ongoing exploration of the calculations and potential errors in the original poster's approach.

Contextual Notes

There is a noted need for clarity on unit conversions, particularly in converting dimensions from centimeters to meters for proper area calculation. The original poster's initial calculations appear to have been based on incorrect assumptions about the dimensions.

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Homework Statement



A science-fair radio uses a homemade capacitor made of two 45 45 sheets of aluminum foil separated by a 0.30-mm-thick sheet of paper. Assume dielectric constant of paper is 3.0.

What is its capacitance?

Homework Equations



C=k e0 A / d


The Attempt at a Solution



I'm not sure if this is the wrong formula or if I am supposed to double .45m since there are two plates. Anyways, I came up with this...

(3.0) * (8.85*e-12) * (.45) / .0003

But the answer I came up with is wrong. Can anyone steer me in the right direction?
 
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you need the area of the plate in the equation, not the length of the side. 0.45m is the length of the side of the pieces of aluminium foil
 
boom, what willem said. and next time include units on the 45, because that number means nothing to me
 
and next time, if you have the answer in front of you and its a simple calculation such as this. divide your answer by the right answer, or vice versa, and you can figure out the factor that you are off by. and that can be very helpful
 
oh I am sorry, i wrote what i did down wrong. I did do by area -- 45cmx45cm=2025 and that is 20.25 meters. So i multiplied (3.0) * (8.85*e-12) * (20.25m) / .0003 and the answer I got was 1.79*e-6. I know I am messing up a simple calculation somewhere!
 
csimon1 said:
oh I am sorry, i wrote what i did down wrong. I did do by area -- 45cmx45cm=2025 and that is 20.25 meters. So i multiplied (3.0) * (8.85*e-12) * (20.25m) / .0003 and the answer I got was 1.79*e-6. I know I am messing up a simple calculation somewhere!

UNITS! If you are working in SI, then your area needs to be in m2:

45cm x 45cm is equivalent to 0.45m x 0.45m = 0.2025m2

Now try with that.
 

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