Parallel plate capacitor voltage question

[needhelpplease]

Homework Statement

A parallel-plate capacitor is connected to a 100 V battery until it is fully charged. The distance between the plates is d and the space between the plates is filled with air (k=1.0). Then, the battery is disconnected. If the distance between the plates is increased to 3d, the voltage of the capacitor will be ?

Homework Equations

C=ɛ0*A/d
C=Q/V
U=QV/2
E=V/d

The Attempt at a Solution

So i know that capacitance is inversely prop. to distance. so if distance is tripled then capacitance will be 1/3 C but i cannot relate that to voltage. I know the correct answer is 33V but i cannot get my head about it. I know that if i multiply 100*1/3 i will get 33V but how does multiplying capacitance (F)by volts will give me volts.[/B]

 

[cnh1995]

Homework Statement

A parallel-plate capacitor is connected to a 100 V battery until it is fully charged. The distance between the plates is d and the space between the plates is filled with air (k=1.0). Then, the battery is disconnected. If the distance between the plates is increased to 3d, the voltage of the capacitor will be ?

Homework Equations

C=ɛ0*A/d
C=Q/V
U=QV/2
E=V/d

The Attempt at a Solution

So i know that capacitance is inversely prop. to distance. so if distance is tripled then capacitance will be 1/3 C but i cannot relate that to voltage. I know the correct answer is 33V but i cannot get my head about it. I know that if i multiply 100*1/3 i will get 33V but how does multiplying capacitance (F)by volts will give me volts.[/B]

Which quantity remains the same in both the cases?

 

[needhelpplease]

Which quantity remains the same in both the cases?

Area i believe?

 

[cnh1995]

Area i believe?

..and??

 

[needhelpplease]

..and??

Area and k (dielectric)

 

[cnh1995]

Area and k (dielectric)

Ok. What about charge?

 

[needhelpplease]

Charge is not related?

 

[cnh1995]

Charge has nowhere to go I believe. So wouldn't it remain consatnt?

Charge is not related?

V=Q/C.

 

[needhelpplease]

I GOT IT. Thank you.

So as distance becomes tripled. capacitance becomes 1/3 and since capacitance is inversely proportional to voltage. so C goes 1/3 voltage is multiplied by 3 so 100*3=300V