please explain me this two questions in detail. I have already known the answer,

Question

please explain me this two questions in detail. I have already known the answer, but I need to be taught what is really going on in this two question. cheers

A parallel-plate capacitor is connected to a battery. The energy of the capacitor is U0. The capacitor remains connected to the battery while the plates are slowly pulled apart until the plate separation doubles. The new energy of the capacitor is U. Find the ratio U/U0.

0.5

A parallel-plate capacitor is connected to a battery. The energy of the capacitor is U0. The capacitor is then disconnected from the battery and the plates are slowly pulled apart until the plate separation doubles. The new energy of the capacitor is U. Find the ratio U/U0.

2

0.5

Explanation / Answer

Part A)

Since Uo = .5CV2 and C = eA/d, we can get this...

Uo = .5eAV2/d

In this form, we see that Uo and d are inversely proportional. Thus if d doubles, Uo must decrease by that amount, thus Uo is cut in half, so the new U is half the original.

That means U/Uo = .5

Part B)

In this case, Uo = .5CV2 and V = Ed since voltage will change this time since the battery is no longer supplying a constant voltage

Uo = .5eA/d(E2d2)

Uo = .5eAE2d

In this instance Uo and d are directly proportional, so if d doubles, Uo must also double. Thus the new U is twice the original

U/Uo = 2

Related Questions

Navigate

• Browse (All)
• Browse P
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.