A battery is permanently connected to a parallel plate capacitor and the energy stored is x joules. When one plate is moved so that the separation of the plate is doubled, the energy now stored in the joule is:
Correct answer: C. x/2
- A. 4x
- B. 2x
- C. x/2
- D. x/4
Explanation
C = Aπ / d where C is capacitance, π is the permittivity of free space, A is the area of plates, and d is the distance between them. When d is doubled, C halves.Since v remains constant throughout because the battery is permanently connected to the capacitor we use the formula E= Cv^2 / 2 where E is energy stored in a capacitor, C is capacitance, and v is the potential difference. So when C halves, E halves because C and E are directly proportional. So the answer is x/2 which is option C.
This question appeared on the ETEA MDCAT 2015 paper, which you can sit online with every answer explained.
Report an error
The more specific you are, the faster it gets fixed. A source beats an opinion.
Prefer email? [email protected]
About Capacitors
Capacitors store electric charge and energy in an electric field between conductors. Work includes capacitance, the relation Q = CV, dielectric materials, charging and discharging, energy formulas, and combinations of capacitors in series and parallel. Electric potential difference is needed to understand why charge and stored energy change.
Practise Electrostatics
831 free Electrostatics MCQs from Physics, each with the correct answer and an explanation. Unlimited attempts, no account needed.
Discussion
Stuck on an option, or know a faster way to get there? Ask or explain it here.
No comments yet. Be the first to explain this one.
Exams that ask Physics questions like this
Physics is on 16 papers prepared for on TestUstad, and all of them draw the same bank, so this question is worth knowing for every one of them.
More Capacitors questions
The electric field between the plates of an isolated air-spaced parallel- plate capacitor is E. What is the field between the plates after immersing the capacitor in a liquid of relative permitivity 10?
A capacitor which has a capacitance of 1 farad (F) will:
The energy stored in a charged capacltor is given by:
A charged capacitor stores 10 C at 40 V.. Its stored energy is:
The potential of the two plates of a capacitor are +10 V and -10 V the charge on one of the plates is 40C . The capacitance of the capacitor is :
When dielectric is removed from plates of a charged capacitor then electric field between plates: