JEE Main · 2020 · 07 Jan 2020 · Shift 2 · Capacitance

WhatsApp Email

A 60 pF capacitor is fully charged by a 20 V supply. It is then disconnected from the supply and is connected to another uncharged 60 pF capacitor in parallel. The electrostatic energy that is lost in this process by the time the charge is redistributed between them is (in nJ) ______.

Answer: 6

Solution

The capacitor first stores

U_{i} = \frac{1}{2} C V^{2} = \frac{1}{2} (60 \times 1 0^{- 12}) (20)^{2} = 12

nJ. When it is joined to an identical uncharged capacitor the same charge now spreads over twice the capacitance, so the common voltage falls to

V = \frac{60 \times 20}{120} = 10

V. The energy it holds afterwards is

U_{f} = \frac{1}{2} (120 \times 1 0^{- 12}) (10)^{2} = 6

nJ, so the energy quietly lost while the charge redistributes is

12 - 6 = 6

nJ.

JEE Main · 2020 · 07 Jan 2020 · Shift 2 · Integer answer

Practise more: all JEE Main PYQs on Capacitance →

More JEE Main questions on Capacitance

A capacitor $P$ with capacitance $10 \times 1 0^{- 6} F$ is fully charged with a potential difference of 6.0 V and disconnected from the battery. The charged capacitor $P$ is connected across another capacitor $Q$ with capacitance $20 \times 1 0^{- 6} F$ . The char …
JEE Main 2026View solution →
The space between the plates of a parallel-plate capacitor of capacitance C (without any dielectric) is now filled with three dielectric slabs of dielectric constants $K_{1} = 2, K_{2} = 3$ , and $K_{3} = 5$ (as shown in the figure). If new capacitance is …
JEE Main 2026View solution →
A parallel plate capacitor with plate separation 5 mm is charged by a battery. On introducing a mica sheet of 2 mm and maintaining the connections of the plates with the terminals of the battery, it is found that it draws $25%$ more charge from the battery. The dielectric con …
JEE Main 2026View solution →
Three parallel plate capacitors each with area A and separation d are filled with two dielectric (k₁ and k₂) in the following fashion. Which of the following is true? (k₁ > k₂)
JEE Main 2026View solution →
Identify the correct statements :
A. Effective capacitance of a series combination of capacitors is always smaller than the smallest capacitance of the capacitor in the combination.
B. When a dielectric medium is placed between the charged plates of a capacitor, displacement of c …
JEE Main 2026View solution →
A parallel plate capacitor has capacitance C , when there is vacuum within the parallel plates.
A sheet having thickness $(\frac{1}{3})^{rd}$ of the separation between the plates and relative permittivity K is introduced between the plates. The new capacitan …
JEE Main 2026View solution →