Physics - Capacitance

Question - 1

Three identical capacitors are connected together differently. For the same voltage to every combination, the one that stores maximum energy is

  • A the three in series
  • B the three in parallel
  • C two in series with the third in parallel with it
  • D two in parallel with the third in series with it

Question - 2

Two condensers of capacities 2C and C are joined in parallel and charged upto potential V. The battery is removed and the condenser of capacity C is filled completely with a medium of dielectric constant K. The potential difference across the capacitors will now be

  • A \(\frac { 3V }{ K+2 } \)
  • B \(\frac { 3V }{ K}\)
  • C \(\frac { V }{ K+2 } \)
  • D \(\frac { V }{ K } \)

Question - 3

A capacitor with capacity 100 \(\mu F\) is charged with a battery of 24 V. It is then connected to a battery of 12 V with positive plate is joined to positive terminal of battery. Heat developed in the process of flow of charge after connection is

  • A greater than 7.2 mJ
  • B less than 7.2 mJ
  • C equal to 7.2 mJ
  • D No heat is produced

Question - 4

A capacitor is made of two circular plates of radius R each, separated by a distance d << R. The capacitors is connected to a constant voltage. A thin conducting disc of radius r << R and thickness t << r is placed at a centre of the bottom plate. Then, the minimum voltage required to lift the disc, if the mass of the disc is m, is

  • A \(\sqrt { \frac { mg{ d }^{ 2 } }{ \pi { \varepsilon }_{ 0 }{ r }^{ 2 } } } \)
  • B \(\frac { { \varepsilon }_{ 0 }\sigma }{ d } \)
  • C \(\frac { \sigma }{ { \varepsilon }_{ 0 } } d\)
  • D None of these

Question - 5

Match the value of capacitance given in Column I with their values given in Column II and select the correct option from the choices given below

Column I Column II
A. Capacitance of parallel plate capacitor in air 1. \(\frac { K{ \varepsilon }_{ 0 }A }{ d } \)
B. Capacitance of parallel plate capacitor when a dielectric slab is inserted partially between the plates 2. \(\frac { { \varepsilon }_{ 0 }A }{ \left( d-t \right) +\frac { t }{ K } } \)
C. Capacitance of parallel plate capacitor when a dielectric slab is inserted fully between the plates. 3. \(\frac { { \varepsilon }_{ 0 }A }{ d } \)
  • A A B C 1 2 3
  • B A B C 3 2 1
  • C A B C 3 2 1
  • D A B C 2 3 1

Question - 6

A parallel plate condenser with a dielectric of dielectric constant K between the plates has a capacity and is charged to a potential V volt. The dielectric slab is slowly removed from between the plates and then reinserted. The net work done by the system in this process is

  • A \(\frac { 1 }{ 2 } \left( K-1 \right) { CV }^{ 2 }\)
  • B \({ CV }^{ 2 }\left( K-1 \right) K\)
  • C \(\left( K-1 \right) { CV }^{ 2 }\)
  • D zero

Question - 7

A fully charged capacitor has a capacitance C. It is discharged through a small coil of resistance wire embedded in a thermally insulated block of specific heat capacity s and mass m. If the temperature of the block is raised by \(\triangle T\), the potential difference V across capacitance is

 

  • A \(\sqrt { \frac { 2mC\triangle T }{ s } } \)
  • B \(\frac { mC\triangle T }{ s } \)
  • C \(\frac { ms\triangle T }{ C } \)
  • D \(\sqrt { \frac { 2ms\triangle T }{ C } } \)
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