JEE Physics - Capacitance and capacitor

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Question - 1

In the given circuit, charge Q2 on the \(2 \mu \mathrm{F}\) capacitor changes as C is varied from \(1 \mu \mathrm{F} \text { to } 3 \mu \mathrm{F} \text {. }\)Q2  as a function of 'C' is given properly by (figures are drawn schematically, and are not to scale)

  • A
  • B
  • C
  • D

Question - 2

In the circuit shown in figure, the growth of charge (q) on the capacitor is represented by

  • A \(q=2 E C\left(1-e^{-t / R C}\right)\)
  • B \(q=E C e^{-t / R C}\)
  • C \(q=E C\left(1-e^{-t / R C}\right)\)
  • D \(q=E C\left(1-e^{-t / 2 R C}\right)\)

Question - 3

Charge stored by the \(1.5 \mu \mathrm{F}\) capacitor in the steady state circuit shown is 

  • A \(5 \mu \mathrm{C}\)
  • B \(7.5 \mu \mathrm{C}\)
  • C \(2.5 \mu \mathrm{C}\)
  • D Zero

Question - 4

A circuit is connected as shown in the figure with the switch S open. When the switch is closed, the total amount of charge that flows from y to x 

  • A 0
  • B \(54 \mu \mathrm{C}\)
  • C \(27 \mu \mathrm{C}\)
  • D \(81 \mu \mathrm{C}\)

Question - 5

If key K1 is closed in circuit shown in figure and galvanometer doesn't give deflection at any time, then value of C is

  • A \( 3 \mu F \)
  • B \(9 \mu F \)
  • C \(4 \mu F \)
  • D \(1 \mu F \)

Question - 6

Calculate the capacitance of a parallel plate condenser, with plate area A and distance between plates 4 when filled with a dielectric whose dielectric constant varies as:
\(( \epsilon(x)=\epsilon_{0}+\beta x, 0 \)
\((\epsilon(x)=\epsilon_{0}+\beta(d-x), \frac{d}{2}\)
For what value of would the capacity of the condenser twice that when it is without any dielectric?

  • A \(\beta=\frac{4 \in_{0}}{d} \ln \left(\frac{\epsilon_{0}+\beta \frac{d}{2}}{\epsilon_{0}}\right)\)
  • B \(\beta=\frac{\epsilon_{0}}{d} \ln \left(\frac{\epsilon_{0}+\beta \frac{d}{2}}{\epsilon_{0}}\right)\)
  • C \(\beta=\frac{\epsilon_{0}}{2 d} \ln \left(\frac{\epsilon_{0}+2 \beta D}{\epsilon_{0}}\right)\)
  • D \(\beta=\frac{\epsilon_{0}}{4 d} \ln \left(\frac{\epsilon_{0}+\beta D}{\epsilon_{0}}\right)\)

Question - 7

A capacitor consists of two stationary plates shaped as a semicircle of radius R and a movable plate made of dielectric with relative permittivity e and capable of rotating about an axis O between the stationary plates (figure). The thickness of the movable plate is equal to d which is practically the separation between the stationary plates. A potential difference Zis applied to the capacitor. Find the
magnitude of the moment of forces relative to the axis O acting on the movable plate in the position shown in the figure

  • A \(\frac{(\in-1) \in_{0} R^{2} V^{2}}{2 d}\)
  • B \(\frac{(\in-1) \epsilon_{0} R^{2} V^{2}}{4 d}\)
  • C \(\frac{(\in-1) \in_{0} R^{2} V^{2}}{2 d^{2}}\)
  • D \(\frac{(\in-1) \in_{0} R^{2} V^{2}}{4 d^{2}}\)

Question - 8

The gap between the plates of a parallel-plate capacitor is filled with isotropic dielectric whose permittivity e varies linearly from \(\epsilon_{1} \text { to } \epsilon_{2}\left(\epsilon_{2}>\epsilon_{1}\right)\) in the direction perpendicular to the plates. The area of each plate is equal to S, the separation between the plates is equal to d. Find the capacitance of the capacitor. 

  • A \(C=\frac{\left(\epsilon_{2}-\epsilon_{1}\right) \epsilon_{0} S}{d \ln \frac{\epsilon_{2}}{\epsilon}}\)
  • B \(C=\frac{\left(\epsilon_{2}-\epsilon_{1}\right) \epsilon_{0} S}{4 d \ln \frac{\epsilon_{2}}{\epsilon}}\)
  • C \(C=\frac{\left(\epsilon_{2}-\epsilon_{1}\right) \epsilon_{0} S}{3 d \ln \frac{\epsilon_{2}}{\epsilon}}\)
  • D None of these

Question - 9

In the circuit shown in the figure, there are two parallel plate capacitors each of capacitance C. The switch S1 is pressed first to fully charge the capacitor C1 and then released. The switch S2 is then pressed to charge the capacitor C2. After some time, S2 is released and then S3 is pressed. After some time

  • A The charge on the upper plate of \(C_{1} \text { is } 2 C V_{0}\)
  • B The charge on the upper plate of \(C_{1} \text { is } C V_{0}\)
  • C The charge on the upper plate of C2 is 0
  • D The charge on the upper plate of \(C_{2} \text { is }-C V_{0}\)

Question - 10

A parallel plate capacitor has a dielectric slab of dielectric constant K between its plates that covers 1/3 of the area of its plates, as shown in the figure. The total capacitance of the capacitor is C while that of the portion with dielectric in between is C1. When the capacitor is charged, the plate area covered by the dielectric gets charge Q1 and the rest of the area gets charge Q2.The electric field in the dielectric is E1 and that in the other portion is E2. Choose the correct option/options, ignoring edge effects.

  • A \(\frac{E_{1}}{E_{2}}=1\)
  • B \(\frac{E_{1}}{E_{2}}=\frac{1}{K}\)
  • C \(\frac{Q_{1}}{Q_{2}}=\frac{3}{K}\)
  • D \(\frac{C}{C_{1}}=\frac{2+K}{K}\)