Electrostatics Question 636

Question: A parallel plate capacitor has plates of area A and separation d and is charged to a potential differenceV . The charging battery is then disconnected and the plates are pulled apart until their separation is 2d . What is the work required to separate the plates?

Options:

A) 2ε0AV2/d

B) ε0AV2/d

C) 3ε0AV2/d

D) ε0AV2/2d

Show Answer

Answer:

Correct Answer: D

Solution:

[d] W=U2U1=q22[1C21C1]

C1=ε0Ad,C2=C12=ε0A2d

q=C1V=ε0AVd

Solve to get W=12ε0AV2d

Alternatively: W=Fd=Q22Aε0d=C12V22ε0Ad=12ε0AV2d



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