How Does Inserting a Dielectric Change Capacitor Voltage?

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Homework Help Overview

The problem involves a capacitor initially charged by a battery and later modified by the insertion of a dielectric material. Participants are discussing how this insertion affects the voltage across the capacitor's plates.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants are examining the relationship between charge, capacitance, and voltage, particularly how the dielectric constant influences these variables. There are questions about the steps taken to arrive at the final voltage calculation and whether the assumptions made are valid.

Discussion Status

Some participants are providing guidance on the relationships between charge and capacitance, noting that the charge remains constant when the capacitor is disconnected from the battery. There is an ongoing exploration of the calculations and potential errors in the values obtained.

Contextual Notes

Participants are considering the possibility of significant figures affecting the final answer, as well as the implications of using a dielectric in the context of the problem.

arod2812
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Homework Statement


An empty capacitor is connected to a 11.7-V battery and charged up. The capacitor is then disconnected from the battery, and a slab of dielectric material (κ = 3.1) is inserted between the plates.
Find the magnitude of the amount by which the potential difference across the plates changes.


Homework Equations


I did the following steps but did not get the right answer. Is there another step to the problem?

The Attempt at a Solution


q=CV, therefore C=q/V
C is affected by the k... therefore C(dielectric)= k*C
then the equation reads: q/V = k (q/11.7)... and the Q's cancel out.

The final equation I worked with is (1/V)=3.1 (1/11.7). The answer I got however is not correct. help.
 
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Looks like you are on the right track. Since Q is constant (no place for the charge to go), CV must be constant. Since C goes up by 3.1x, V must do the inverse. What answer exactly did you try?
 
the answer i tried was 3.77... originally i had tried 36.27 which was wrong. But it turns out that both are wrong. What do you think?
 
Well, that's pretty much what I get for 11.7/3.1. And unless I'm missing something, that seems like the right way to get it -- even talks about using the dielectric insertion method for measuring k here:

http://en.wikipedia.org/wiki/High-k

How many sig figs does this homework program expect? Maybe they just want 3.8V?
 

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